---
title: "Glossary: 773 algorithm and data structure terms explained"
url: https://algopath.pro/glossary
language: en
---

# Glossary: 773 algorithm and data structure terms explained

## A/B testing

a way to compare two versions of something (a web page, a feature) by showing version A to some users and version B to others, then measuring which one performs better.

## Abseil flat_hash_map

a hash table from Google's Abseil C++ library that stores its entries in one flat block of memory for faster lookups.

## Abuse detection

systems that spot bad behavior like spam, fraud, or bots by looking for suspicious patterns in activity.

## Account merging

combining two user accounts that belong to the same person into one, keeping the data from both.

## Ad slots

the reserved spaces on a page or app where advertisements are placed.

## Adjacency lists

a way to store a graph where each item keeps a list of the other items it connects to.

## Algorithm

a step-by-step recipe that turns something you have into the answer you want. Like a cooking recipe, but for data.

## Analytics dashboards

a screen that gathers key numbers about a product or business into charts and tables so people can see how things are going at a glance.

## Analytics grouping

collecting many data records into buckets by some shared value (by day, by country) so you can count or total each group.

## Anomaly detection

automatically finding data points that look unusual compared to the normal pattern, often to catch errors or fraud.

## API rate limiters

a control that caps how many requests a program or user can send to a service in a given time, so no one overloads it.

## Array.indexOf

a JavaScript array method that returns the position of a value in an array, or -1 if it isn't there.

## Aspect ratios

the width-to-height proportion of an image or screen, like 16:9, used to keep pictures from stretching.

## ATM cash dispensing

the part of a cash machine that works out which bills to hand you for a requested amount, using as few notes as possible.

## Autocomplete

the feature that suggests or finishes what you're typing based on the first few letters, in search boxes and editors.

## Autocorrect

the feature that automatically fixes misspelled words as you type by matching them to known words.

## Availability grids

a table showing which time slots are free or taken, used in booking and scheduling tools.

## AVL indexes

database indexes built on AVL trees, a self-balancing tree that keeps lookups fast by staying evenly shaped as data is added.

## AVL trees

a kind of search tree that rebalances itself after every insert or delete so it never gets lopsided, keeping searches fast.

## Backtracking

trying a choice, and if it leads to a dead end, stepping back and trying another - like finding your way out of a maze.

## Backup dedup

storing backups without keeping duplicate copies of identical data, so the same block is saved once and reused.

## BFS (breadth-first search)

exploring outward one ring at a time using a queue, like ripples spreading on water. Finds the shortest path when every step counts equally.

## Big-O

a quick way to say how much slower a method gets as the input grows. O(n) means "twice the data, twice the work." O(n^2) means "twice the data, four times the work." O(log n) means "twice the data, just one extra step." It's about the shape of the growth, not seconds on a clock.

## Binary search

finding something in a sorted list by cutting the search area in half each guess, like the "higher / lower" number game.

## Binary search tree (BST)

a tree kept in order (smaller on the left, bigger on the right) so you can find things fast.

## Bioinformatics

the field that uses computer methods to analyze biological data such as DNA and protein sequences.

## Bipartite matching

pairing items from two separate groups (like workers and jobs) so each pair is compatible and as many as possible are matched.

## Bitmask

using the on/off bits inside a single number as a compact row of yes/no switches.

## Bloom filters

a compact structure that quickly tells you whether an item is probably in a set or definitely not, using little memory but allowing rare false positives.

## Board-game scans

checking the squares of a game board (for wins, moves, or matches) by walking across the grid.

## Boggle-style validators

code that checks whether a word can be formed by connecting adjacent letters on a grid, as in the game Boggle.

## Booking systems

software that reserves things like seats, rooms, or appointments and prevents two people from taking the same slot.

## Bounded log tails

keeping only the most recent lines of a log, so older entries drop off once a fixed limit is reached.

## Browser history

the record of pages you've visited, letting you go back and forward through them.

## Brute force

the obvious solution that just tries every possibility. It always works, but it's often slow.

## Bucketed stats

grouping measurements into ranges (buckets) and counting how many fall in each, as in a histogram.

## Budget allocation

deciding how to split a fixed amount of money across competing needs to get the most value.

## Build systems

tools that turn source code into a finished program, running the needed steps in the right order.

## Build tools

programs that automate compiling, packaging, and preparing software for release.

## C qsort

the standard sorting function in the C language's library, which orders the elements of an array.

## C++ make_heap

a C++ standard-library function that rearranges a range of items into a heap, a shape that keeps the largest (or smallest) item easy to reach.

## Cache invalidation

removing or refreshing cached data once it's out of date, so users don't see stale results.

## Cache sharding

splitting a cache across several servers so each holds part of the data and the load is spread out.

## Caching ASTs

saving the parsed form of code (its abstract syntax tree) so a tool doesn't have to re-parse the same source again.

## Calendar booking

reserving a time slot on a calendar while making sure it doesn't clash with an existing one.

## Calendar free/busy

the view that shows which times a person is available or occupied without revealing event details.

## Calendar overlaps

detecting when two calendar events cover the same time, so you can flag or prevent double-booking.

## Call stacks

the running list of functions a program has entered but not yet finished, tracked so it knows where to return.

## Canary deploys

releasing a new version to a small share of users first, watching for problems before rolling it out to everyone.

## Capacity planning

working out how much hardware or resources you'll need to handle expected future demand.

## Cargo loading

deciding how to pack items into a limited space (a truck, container, or ship) to fit the most or the most valuable load.

## Case-insensitive login

accepting a username or email regardless of capital letters, so "Sam" and "sam" are treated as the same.

## Cash registers

the till in a shop that totals a sale and calculates the change to give back.

## Chip routing

laying out the wire connections between components on a computer chip so signals reach where they need to go.

## CI test matrices

a grid of configurations (different versions, operating systems) that automated testing runs against, so code is checked on every combination.

## Circular buffers

a fixed-size storage that reuses its space in a loop, overwriting the oldest data once it fills up.

## Circular imports

when two code files each depend on the other, forming a loop that can break loading; tools detect it.

## Cloud cost caps

limits set on cloud spending so a service automatically slows or stops before the bill goes over budget.

## Clustering

grouping data points that are similar to each other, so natural categories emerge without labeling them by hand.

## Cocktail sort

a sorting method that passes back and forth through a list, bubbling large items up and small items down each way.

## Community detection

finding tightly connected groups within a network, like clusters of friends in a social graph.

## Compilers

programs that translate source code written by people into machine code a computer can run.

## Computer vision filters

operations applied to an image (blur, sharpen, edge-find) that transform each pixel based on its neighbors.

## Config lists

lists of settings that tell a program how to behave.

## Config stores

a central place that holds an application's settings so services can read them consistently.

## Config-drift detection

noticing when a system's actual settings have wandered away from the intended configuration.

## Consistent hashing

a way to spread data across servers so that adding or removing a server moves as little data as possible.

## CPython dict

the dictionary type in CPython, the standard Python, which stores key-value pairs using a hash table for fast lookup.

## Cryptography

the practice of encoding information so only the intended party can read it, used to keep data secret and verify identity.

## Cryptography key-gen

generating the secret keys used to encrypt and decrypt data, usually from large random numbers.

## Currency arbitrage

spotting a chain of currency exchanges that ends with more money than you started, exploiting price differences.

## Cutting stock

working out how to cut standard-size material (paper rolls, metal sheets) into ordered pieces with the least waste.

## Data sharding

splitting a large dataset across multiple databases or servers so each holds only a piece.

## Data structure

a way of arranging things so you can get at them quickly. A shopping list, a phone book, and a stack of plates each arrange stuff for a different job.

## Database B-trees

the balanced tree structure databases use for indexes, keeping data sorted so lookups and ranges stay fast even with huge tables.

## Database compaction

merging and cleaning a database's storage files to reclaim space and remove deleted or outdated entries.

## Database indexes

extra lookup structures a database keeps so it can find rows quickly without scanning the whole table.

## Database sorts

the operation a database uses to put query results in order, for example by date or name.

## Databases

systems that store, organize, and retrieve large amounts of data reliably.

## Datacenter routing

directing network traffic along paths between the many machines in a datacenter.

## DB migrations

scripted changes to a database's structure, applied in order so the schema evolves safely over time.

## Deadlock detection

finding situations where processes are each waiting on the other and none can proceed, so the system can break the standoff.

## Deduplication

removing duplicate copies of the same data so only one is kept.

## Dependency graphs

a map of what depends on what (packages, tasks, files), used to work out a safe build or install order.

## Dependency resolvers

tools that pick a compatible set of package versions so everything a project needs works together.

## Deque

a line you can add to and take from at both ends.

## DFS (depth-first search)

following one path as far as it goes before backing up to try another, using recursion or a stack.

## Diffie-Hellman

a method that lets two parties agree on a shared secret key over an open connection without anyone listening in learning it.

## Dijkstra

an algorithm that finds the shortest path from one point to all others in a network of weighted connections.

## Disk-usage tools

programs that show what's taking up space on a drive by adding up the sizes of files and folders.

## Distinct-count windows

counting how many unique items appeared within a recent time span, like unique visitors in the last hour.

## DNA alignment

lining up two DNA sequences to find where they match and differ, used to compare genes.

## DOM node bookkeeping

keeping track of the elements in a web page's structure as they're added, changed, or removed.

## DOM serialization

turning a web page's in-memory element tree back into HTML text.

## DOM traversal

walking through the elements of a web page's tree to find or process specific nodes.

## DOM trees

the tree-shaped structure a browser builds from a web page, where each HTML element is a node with parents and children.

## Double-booking checks

verifying that a new reservation doesn't overlap one already made for the same resource.

## DP solvers

programs that solve problems with dynamic programming, breaking a big problem into smaller overlapping subproblems and reusing their answers.

## du command

a Unix command that reports how much disk space files and folders use.

## Dynamic programming (DP)

solving a big problem by solving its small overlapping pieces once, writing each answer down, and reusing it instead of redoing the work.

## Edge case

a weird input that trips up sloppy code: nothing at all, just one item, everything the same, or no valid answer.

## Editor bracket matching

the editor feature that highlights the opening bracket paired with the one at your cursor, so you can see if they're balanced.

## Editor find

the search feature in a text editor that locates where a word or phrase appears in the file.

## Editors

programs for writing and changing text or code.

## Embedded sorting

sorting done inside small hardware devices like sensors or appliances, where memory and processing power are tight so the sort has to be lean.

## Embedded systems

small computers built into a device (a car, a washing machine, a thermostat) to control it, rather than a general-purpose PC.

## Error detection

checking whether data got corrupted while stored or sent, so a system can catch mistakes instead of trusting bad data.

## Error-correcting codes

extra bits added to data that let a system not only spot corruption but repair it without asking for the data again.

## Exam timetabling

scheduling exams into time slots and rooms so no student has two exams at once and no room is double-booked.

## External merge sort

a way to sort more data than fits in memory by sorting it in chunks on disk and then merging those sorted chunks together.

## External sort

sorting data that is too big to fit in memory, so it lives on disk and is processed in pieces.

## Feature flags

on/off switches in software that turn features on or off without shipping new code, used to roll features out gradually or hide unfinished ones.

## Feature-flag combos

the different combinations of feature flags that can be on at the same time, which have to be tested because features can interact.

## Feed trimming

cutting an activity feed or timeline down to a fixed number of recent items so it doesn't grow forever.

## File explorers

the program that shows your folders and files and lets you open, move, and delete them (like Finder on Mac or File Explorer on Windows).

## Filesystem walkers

code that visits every folder and file under a starting directory, one after another, to process or list them all.

## Firewall IP ranges

blocks of network addresses a firewall allows or blocks, used to decide which computers may connect.

## Fixed-width ids

identifiers that always use the same number of characters, padded if needed, so they sort and line up neatly.

## Flight itineraries

the full plan of a trip's flights: which planes, in what order, with connections and times.

## Flood fill

the technique that fills a connected area with one color by spreading out from a starting point, like the paint-bucket tool in image editors.

## Fraction math

arithmetic with fractions (like 1/3 + 1/4) done exactly, keeping numerator and denominator instead of rounding to a decimal.

## Fraud dedup

removing duplicate fraud alerts or records so the same suspicious event isn't counted or investigated twice.

## Free-list allocators

a memory manager that keeps a list of freed-up memory blocks so it can hand them out again for new requests.

## Fuzzy search

search that still finds matches when the query has typos or isn't spelled exactly the same as the target.

## Game leaderboards

the ranked score table in a game showing who's on top, updated as players earn points.

## Game move generation

working out all the legal moves a player can make from the current position, used by game logic and AI opponents.

## Game pathfinding

working out how a character should move from one spot to another around obstacles in a game world.

## Game reachability

working out which places or states in a game can actually be gotten to from a given point.

## git bisect

a Git command that finds which commit introduced a bug by repeatedly checking a commit halfway through the suspect range.

## git diff

a Git command that shows the exact changes between versions of your files.

## git merge-base

the Git command that finds the most recent common ancestor commit of two branches.

## Go maps

the built-in key-value lookup structure in the Go programming language, used to store and find data by a key.

## Graph

dots joined by lines, where the lines can form loops. Roads between cities, friends on social media, and task dependencies are all graphs.

## Graph diameter

the longest of all the shortest paths in a network, showing how far apart the two most distant points are.

## Greedy

grabbing the best-looking option at each step and hoping the whole result comes out best. Only trustworthy when you can prove it.

## grep

a Unix command that searches text or files for lines matching a pattern.

## Grid path finders

code that finds a route between two cells on a grid of squares, going around blocked cells.

## Grid pathfinding

finding a route from one cell to another across a grid, avoiding blocked squares.

## gzip

a common tool and format for compressing files to make them smaller for storage or transfer.

## Hash table / hash map

a lookup that finds a value by its key almost instantly, like a dictionary where you flip straight to the word. Each language has one: `Map` in JavaScript and TypeScript, `dict` in Python, an array in PHP, `HashMap` in Java.

## Hash tables

a structure that stores data by key so you can look up a value almost instantly instead of scanning everything.

## Hashtag splitting

breaking a run-together hashtag like #ThrowbackThursday into separate words.

## Heap / priority queue

a pile that always hands you the smallest (or biggest) item next, without sorting everything. Good for "top 5" lists and live streams of data.

## heapq.heapify

a Python function that rearranges a list into a heap so you can repeatedly pull out the smallest item efficiently.

## Heatmap rendering

drawing a colored map where color shows intensity, so hot spots (more activity, higher values) stand out.

## Held-Karp TSP

an exact method for the traveling-salesman problem that finds the shortest route visiting every stop once, using stored partial results to avoid redoing work.

## Histograms

a chart that groups numbers into buckets and shows how many fall in each, revealing the shape of the data.

## IDE completion

the code editor feature that suggests and finishes what you're typing (variable names, functions) as you write.

## Idempotency keys

a unique tag on a request so that if it's sent twice by mistake, the server does the action only once (like avoiding a double charge).

## Image labeling

marking the separate objects or regions in an image, for example finding each distinct blob and giving it a number.

## Image processing

changing or analyzing pictures with code: resizing, sharpening, detecting edges, and so on.

## Image rotation

turning a picture by an angle, for example 90 degrees, while keeping it correct.

## In place

changing the original data directly instead of making a copy, to save memory.

## Index validation

checking that a position or lookup key is within the allowed range before using it, so code doesn't read past the end.

## Integral images

a precomputed table over an image that lets you add up the pixels in any rectangle instantly, used to speed up image analysis.

## Introsort

a sorting method that starts fast with quicksort and switches to a safer method if things go badly, so it stays quick without worst-case slowdowns.

## introsort fallback

the safety switch in introsort that swaps to heapsort when quicksort is going too slow, guaranteeing good worst-case speed.

## Intrusion detection

watching a system or network for signs of an attack or break-in and raising an alert.

## Invariant

something you keep true at every step of a loop; it's the reason the loop actually works.

## Inventory holds

temporarily reserving stock (for an order in progress) so two customers can't buy the last item at once.

## Inversion counts

counting how many pairs in a list are out of order, a measure of how unsorted the list is.

## Invoice reconciliation

matching invoices against payments or records to make sure the amounts agree and nothing is missing.

## IP routing

deciding which path a piece of network data should take across the internet to reach its destination address.

## Java HashMap

Java's built-in key-value store, used to save and look up values by a key quickly.

## JavaScript Map

JavaScript's built-in key-value store that remembers insertion order and lets you look up values by any key.

## JavaScript Set

JavaScript's built-in collection that holds only unique values, used to remove duplicates or test membership fast.

## Job assignment

matching workers or machines to tasks in the best way, for example the lowest total cost or time.

## Job pipelines

a chain of processing steps where each job passes through stages in order, one feeding the next.

## Job scheduling

deciding when and in what order tasks run, given deadlines, priorities, and limited resources.

## JPEG

a common file format for photos that shrinks them by dropping detail the eye barely notices, trading some quality for much smaller files.

## JPEG image compression

the method behind JPEG files that makes photos smaller by discarding fine detail people are unlikely to see.

## JSON/XML parsers

code that reads JSON or XML text and turns it into structured data a program can work with.

## k-way merge

combining k already-sorted lists into one sorted list by repeatedly taking the smallest front item across them.

## Kafka partitions

the separate ordered streams a Kafka topic is split into, letting many consumers read data in parallel. (Kafka is a system for moving streams of events between programs.)

## Kafka streams

continuous flows of event data handled by Kafka, read and processed as they arrive rather than in one batch.

## Kruskal MST

an algorithm that connects all points in a network with the least total cabling by adding the cheapest links first and skipping any that would form a loop.

## LCA

lowest common ancestor: in a tree of items, the deepest single node that sits above two given nodes, used to find their nearest shared parent.

## Leaderboards

a ranked list showing who or what scores highest, updated as new results come in.

## Ledger reconciliation

checking two sets of financial records against each other to confirm every entry matches and the balances agree.

## Linux kernel

the core of the Linux operating system that manages memory, files, and hardware and lets programs run.

## Linux rb_tree

the red-black tree used inside the Linux kernel, a self-balancing sorted structure that keeps lookups and inserts fast.

## Live feeds

streams of content that update in real time, like a news or social feed adding new items as they happen.

## Load balancing

spreading incoming requests across several servers so no single one gets overwhelmed.

## Log aggregation

collecting log messages from many machines and services into one place so you can search and analyze them together.

## Log dedup

removing repeated log lines so the same message isn't stored or shown many times.

## Log merging

combining log entries from several sources into one stream, usually kept in time order.

## Log pipelines

the chain of steps that collects, filters, and stores log data as it flows from apps to a searchable store.

## Log redaction

hiding or blanking out sensitive details (passwords, card numbers) in logs before they're stored or shared.

## Log scanning

reading through log files to find specific entries, patterns, or problems.

## Log viewers

a tool for browsing, searching, and filtering log messages.

## lower_bound/upper_bound

C++ search functions on sorted data that find the first position at or above a value and the first position strictly above it.

## LRU caches

a cache that, when it runs out of room, throws out the item you used least recently to make space, keeping the things you touch often.

## LSM compaction

the background cleanup in log-structured storage that merges many small sorted files into fewer bigger ones and drops stale data, keeping reads fast.

## Machine scheduling

deciding which machine does which job and when, to finish work as fast or as cheaply as possible.

## Making change

working out which coins or notes add up to a given amount, usually with the fewest pieces.

## Map navigation

finding and following a route between two places on a map, with turn-by-turn directions.

## Matrix chain

the problem of choosing the order to multiply a series of matrices so the total work is smallest.

## Matrix display

showing a grid of values on screen, often as a table or an image.

## Matrix serialization

turning a grid of values into a flat sequence of bytes or text so it can be saved or sent, and read back later.

## Maze generation

creating a maze automatically with a guaranteed path through it, used in games and puzzles.

## Median filters

an image or signal cleanup that replaces each value with the middle value of its neighbors, good at removing speckle noise.

## Meeting rooms

scheduling meetings into rooms so no two overlapping meetings land in the same room.

## Memoization

remembering answers you already worked out, so asking the same question again is instant. It's the first step from recursion toward dynamic programming.

## Memory allocators

the part of a system that hands out and reclaims chunks of memory as programs ask for and release them.

## Merge sort

a sorting method that splits the list in half, sorts each half, then merges the two sorted halves back together.

## Message brokers

middleman software that takes messages from senders and delivers them to the right receivers, so programs can talk without connecting directly.

## Metric baselines

the normal expected level of a measurement, used to judge whether a new reading is unusually high or low.

## Metrics dashboards

a screen of charts and numbers showing how a system is performing at a glance.

## Metrics monitoring

continuously tracking measurements from a system and alerting when something looks wrong.

## Metrics peaks

the highest points in a stream of measurements, useful for spotting spikes in load or usage.

## Metrics rollups

the periodic squashing of many raw data points into summary numbers (like per-minute averages) so charts and reports stay small and fast.

## Modular arithmetic

counting that wraps around, like a clock rolling from 12 back to 1. Used to keep giant numbers from getting out of hand.

## Module bundlers

tools that take all the separate code files a web app is made of and combine them into a few optimized files a browser can load quickly.

## Monotonic stack/queue

a stack or queue you keep in order as you add to it, so you can instantly find the next bigger (or smaller) item.

## Moving averages

an average recalculated over the most recent stretch of values as new ones arrive, used to smooth out noisy data and show the trend.

## n

how big the input is: the number of items you're working with.

## Navigation engines

the software behind turn-by-turn directions that figures out the best route from where you are to where you want to go.

## Near-sorted leaderboards

score rankings that are already almost in order, so only a few entries need to shift when a new score comes in.

## Negative case

a test where the right answer is "nothing found" or "not possible," to check the code handles the empty or failure case, not just the happy one.

## Network buffers

small holding areas in memory where incoming or outgoing network data waits its turn to be processed or sent.

## Network cabling

the physical wires connecting computers and equipment so they can pass data to each other.

## Network diameter

the longest shortest-path between any two points in a network, telling you the worst-case number of hops a message might take.

## Observability dashboards

screens that show live charts and numbers about how a running system is behaving, so operators can spot problems.

## OLAP cubes

pre-computed tables of business numbers grouped by several dimensions at once (time, region, product) so analytical reports come back instantly.

## One-stroke drawing

tracing a shape without lifting the pen or repeating any line, a puzzle that maps to finding a path through every edge of a graph once.

## Order books

the live list of all buy and sell offers for a stock or other asset, sorted by price, that a market uses to match trades.

## Org charts

a diagram of who reports to whom in a company, shaped as a tree from the top down.

## OS schedulers

the part of an operating system that decides which program gets to use the CPU next and for how long.

## OSPF routing

a method routers use to learn the network layout and pick the shortest path for sending data across a large network.

## Overbooking detection

checking whether more reservations have been accepted than there is capacity for, such as too many bookings for the seats available.

## p50 monitoring

tracking the median (50th percentile) of a measurement, so half the values fall below it, used to watch typical response times.

## Paint bucket

the drawing-tool feature that fills a connected area of the same color with a new color when you click inside it.

## Pairwise testing

a way to cut down test cases by checking every pair of input combinations at least once instead of all possible combinations.

## Palindrome checks

testing whether a word or sequence reads the same forwards and backwards, like "level".

## Payment matching

lining up incoming payments with the invoices or orders they are meant to settle.

## Payment terminals

the card-reader devices in shops that take a customer's card and process the payment.

## Peak-load detection

spotting the moments when demand on a system is highest, so you can size capacity or trigger alerts.

## Percentile queries

questions like "what value is greater than 95% of the data", used to summarize things like response times.

## Percolation

a model of whether connected paths span across a grid, used to study when scattered links suddenly join into one large network.

## Permission trees

access rights arranged in a hierarchy where a folder or group's settings carry down to everything nested inside it.

## Plagiarism detection

comparing a document against others to find copied or closely matching passages.

## PNG

a common image file format that stores pictures without losing quality, often used for graphics and screenshots.

## Pointer / index

a marker for a spot in a list, like a finger pointing at one item. "Move the pointer" means point at a different spot.

## Prefix sum

a running total written down at each spot, so the sum of any stretch is one subtraction of two totals. Like a bank balance: the change over a period is the end balance minus the start balance.

## Price feeds

a continuous stream of the latest prices for stocks, currencies, or goods, delivered to trading and pricing systems.

## Print spoolers

the system that queues up print jobs and sends them to the printer one at a time in order.

## Private class fields

variables inside a code object that only that object's own methods can read or change, hidden from outside code.

## Producer batching

grouping many small produced items together and sending them as one batch to cut per-item overhead.

## Puzzle solvers

programs that search through possible moves to find a solution to a puzzle like a maze or Sudoku.

## Python dict

Python's built-in structure for storing key-to-value pairs, letting you look up a value fast by its key.

## Python heapq

a Python library that keeps a list arranged so the smallest item is always quick to grab, used for priority queues.

## Query builders

code tools that assemble database queries piece by piece instead of writing the query text by hand.

## Query planners

the database component that works out the fastest way to run a query before actually running it.

## Queue

a line where the first to arrive is the first served, like a queue at a shop.

## quickselect

a method that finds the k-th smallest item in a list without fully sorting it, by repeatedly partitioning around a pivot.

## Quorum selection

requiring that a minimum number of servers in a group agree before an action counts, so the system stays consistent.

## Race-condition testing

deliberately checking what happens when two parts of a program touch the same data at the same time, to catch timing bugs.

## Radix-sort phase

one pass of radix sort, a sorting method that orders numbers by looking at one digit at a time.

## Range indexes

a database structure that quickly finds all records whose value falls between two bounds.

## Range-min queries

questions asking for the smallest value within a given slice of a list, answered fast with the right preparation.

## Rate tables

lookup tables of prices or charges, such as shipping or currency rates, used to compute a cost for given inputs.

## Rate-limit budgets

the allowance of how many requests a user or client may make in a time window before being throttled.

## Rate-limit tuning

adjusting those request allowances to balance protecting a system against letting legitimate traffic through.

## React reconciler

the part of the React web framework that compares the new interface to the old one and updates only what changed on screen.

## React useMemo

a React feature that remembers the result of a costly calculation and reuses it instead of redoing it on every render.

## Record clustering

grouping database records that are similar to each other, for example customers with alike behavior.

## Record deduplication

finding and merging duplicate entries that refer to the same real thing, like the same person listed twice.

## Recursion

a function that solves a big problem by calling itself on a smaller piece, until the piece is tiny enough to answer directly.

## Red-black trees

a self-balancing sorted tree that rearranges itself as you add or remove items so lookups stay fast no matter the order they arrive.

## Reduce phase

the stage in a MapReduce data job that combines many partial results into the final totals.

## Register allocation

the compiler's job of deciding which of a CPU's few fast storage slots (registers) each value should live in while a program runs.

## Replay detection

spotting when someone resends a captured request or message to catch attempts to reuse it fraudulently.

## Resource planning

working out how to assign limited resources like people, machines, or time across the work that needs them.

## Response caches

stored copies of previous replies so a repeat request can be answered instantly without redoing the work.

## Retry budgets

a cap on how many times failed operations may be retried, to stop a struggling system from being flooded with retries.

## Ring buffers

a fixed-size buffer that wraps around and overwrites its oldest data when full, used for steady streams like audio or logs.

## Ring indexes

position numbers that wrap back to the start after the end, used to walk in circles around a fixed-size buffer.

## RIP routing

an older, simple method routers use to share which networks they can reach and pick paths by fewest hops.

## RNA folding

predicting how an RNA molecule bends and pairs up with itself, a biology problem solved by matching-up algorithms.

## Road networks

the map data of roads and intersections that routing software searches to plan a drive.

## Robot navigation

a robot working out how to move through its surroundings from one point to another without hitting obstacles.

## Robotics pathing

computing the actual path a robot should follow to reach a goal while avoiding obstacles.

## Role inheritance

an access-control setup where one role automatically gains all the permissions of the roles beneath it.

## Rolling hashes

a way to keep a running fingerprint of a sliding stretch of text, updated cheaply as you move one step, so you can compare substrings fast.

## Rotated logs

log files that are closed and rolled over to a fresh file on a schedule or size limit, so old ones can be archived or deleted.

## Route generation

producing the set of possible paths or turn steps for getting from one place to another.

## Route planning

choosing the best path from a start to a destination given distances, traffic, or other costs.

## Router tables

the lookup list inside a router that says which direction to send data for each destination network.

## Routing tables

the stored map of destinations and the next hop to reach each one, used to forward network traffic.

## RSA

a widely used encryption method that secures data using a public key to lock and a matching private key to unlock.

## rsync

a Unix tool that copies and syncs files between locations, transferring only the parts that changed to save time.

## Saved game state

the stored snapshot of a game's progress so a player can quit and later pick up where they left off.

## Scaffold

the ready-to-run practice setup you get for each step (starter code + tests) so you can jump straight to solving instead of building the setup.

## Scheduling

deciding when and in what order tasks, jobs, or appointments should run given their timing and constraints.

## Screen buffers

the block of memory holding the current picture to be shown on screen, which the display reads from.

## Seam carving

a way to resize an image by removing the least noticeable connected lines of pixels so important content keeps its shape.

## Search indexes

a prepared structure that lets a search engine find matching documents fast instead of scanning everything.

## Search normalization

cleaning up search text (lowercasing, trimming accents, unifying spellings) so different forms of a word still match.

## Search queries

the words and filters a user types to find what they are looking for.

## Search ranking

ordering search results so the most relevant ones appear at the top.

## Search suggestions

the guesses a search box offers as you type, completing or proposing likely queries.

## Session stores

where a web server keeps the temporary data about each logged-in user's current visit, like their cart or login state.

## Set

a bag of items with no duplicates, where "is this in it?" is instant. Each language has one: `Set` in JavaScript and TypeScript, `set` in Python, an array used as a lookup in PHP, `HashSet` in Java.

## Shell tab-completion

the command-line feature that finishes a file name or command for you when you press Tab.

## Signal analysis

examining a measured signal, such as sound or sensor data, to pull out patterns, frequencies, or events.

## Signal processing

transforming and cleaning up signals like audio, images, or sensor readings to filter noise or extract useful information.

## Skip lists

a sorted list with extra express layers of shortcuts over it, so you can jump ahead and find items quickly.

## SLA tracking

measuring whether a service is meeting its promised targets, like uptime or response speed, agreed with customers.

## Sliding window

a stretch of a list, `[left, right]`, that you slide along: add one item on the right, drop one on the left, instead of re-counting the whole stretch each time.

## Sliding-window min

keeping track of the smallest value within a window that slides along a sequence, updated as the window moves.

## Small config lookups

quick reads of a handful of settings values that a program needs to adjust its behavior.

## Small leaderboards

short ranked score lists with few enough entries that keeping them ordered is cheap.

## Social circles

groups of people connected by friendship or contact, modeled as a network to find clusters or mutual links.

## Social graphs

a way of storing who is connected to whom on a network, used by sites like Facebook or LinkedIn to find friends, mutual connections, and suggestions.

## Sorted lookup tables

a list kept in sorted order so you can find any entry quickly by jumping to the middle instead of scanning every row.

## Space complexity

how much extra memory the method needs as the input gets bigger.

## Spell-check

a feature that compares each word you type against a dictionary and flags the ones it doesn't recognize.

## Spellcheckers

the tools inside word processors and browsers that catch misspelled words and suggest corrections.

## Spreadsheet cleanup

the work of fixing a spreadsheet's data, like removing duplicate rows, trimming stray spaces, and correcting formats.

## Spreadsheet search

finding a specific value or row inside a spreadsheet, often much faster when the column is sorted.

## Spreadsheets

grid-based apps like Excel or Google Sheets for storing numbers and text in rows and columns and running calculations on them.

## SQL GROUP BY

a database command that collapses rows sharing the same value into groups so you can total or count each group.

## Stable sort

a sorting method that keeps items with equal keys in their original relative order, so a second sort doesn't scramble the first.

## Stack

a pile where you always take from the top. Think of a stack of plates: the last one on is the first one off.

## std::map

a C++ container that stores key-value pairs sorted by key, letting you look up, insert, and traverse them in key order.

## std::map erase

the C++ operation that removes an entry from a std::map by its key.

## std::priority_queue

a C++ container that always gives you the highest-priority item next, used when you repeatedly need the current maximum (or minimum).

## std::sort

the C++ standard function that sorts a range of items quickly, in place.

## Stock span

a calculation of how many days in a row a stock's price stayed at or below today's price, used in trading charts.

## Stream processing

handling data as it arrives in a continuous flow, instead of waiting to collect it all and process it in one batch.

## Stream sampling

picking a small representative subset from an endless flow of data when you can't store or examine every item.

## Stream windows

grouping a continuous flow of data into time or count chunks (like "the last 5 minutes") so you can summarize each chunk.

## Streaming leaderboards

scoreboards that update live as new results come in, keeping the top players ranked in real time.

## Sudoku solvers

programs that fill in a Sudoku puzzle by trying numbers and backtracking whenever a choice breaks the rules.

## Suffix arrays

a sorted list of all the endings of a piece of text, used to search large texts and match patterns quickly.

## Symbol tables

a lookup structure a compiler or interpreter uses to remember every name in a program (variables, functions) and what each refers to.

## Table column sort

reordering the rows of a table by clicking a column header to sort by that column's values.

## Task assignment

deciding which worker, machine, or server should handle each job, often to balance load or minimize cost.

## Task queues

a waiting line of jobs to be done, so work can be handed out to workers one at a time in order.

## Task schedulers

systems that decide when and in what order pending jobs run, based on priority, timing, or available resources.

## Taxonomy rollups

adding up values along a category tree so a parent category shows the combined totals of everything beneath it.

## TCP flags

small on/off bits in network packets that signal the state of a connection, like starting, acknowledging, or closing it.

## Template engines

tools that fill placeholders in a page or document with real data to produce the final text, used to build web pages from data.

## Test matrices

a grid of all the combinations (browsers, versions, settings) that software is tested against to catch problems in each case.

## Text cleanup

removing unwanted characters, extra spaces, or bad formatting from text so it's consistent and ready to use.

## Text diff

a comparison that shows exactly which lines or words were added, removed, or changed between two versions of text.

## Text editors

programs for writing and editing plain text or code, like Notepad, VS Code, or Vim.

## The DOM

the browser's live, tree-shaped model of a web page that code can read and change to update what you see.

## Tier

how much of the hard part is on you for a step: write the core yourself (1), fix a planted bug (2), or review working code (3).

## Time complexity

how fast the amount of work grows as the input gets bigger.

## Time-series alerting

watching a stream of measurements over time and raising an alarm when a value crosses a set threshold.

## Time-series rollups

summarizing measurements collected over time into coarser buckets (like per-minute into per-hour) to save space and speed up charts.

## Time-series stores

databases built to hold measurements stamped with times, like server metrics or sensor readings, and query them by time range.

## Timer wheels

a data structure that groups many pending timers into slots on a rotating wheel, so a system with thousands of timeouts can fire them efficiently.

## Timsort

a fast sorting method that combines merge sort and insertion sort, used as the default sort in Python and Java.

## Tokenizers

tools that split text into meaningful pieces (words, symbols, or subwords) so a program or language model can process it.

## Top-k queries

requests that return only the highest (or lowest) k items, like the 10 best-selling products, without ranking everything else.

## Topological sort

putting tasks in an order where nothing starts before the tasks it depends on. Like getting dressed: socks before shoes.

## Trading analytics

the calculations and charts traders use to study prices, volumes, and trends and decide when to buy or sell.

## Trading dashboards

live screens that show a trader current prices, positions, and key metrics all in one view.

## Trading SMAs

simple moving averages of a stock's price over a recent window of days, used to smooth out noise and spot trends.

## Transitive closure

working out every point reachable from every other point in a network, following the connections step by step.

## Tree

items linked in a branching shape, each with one parent and some children, and no loops. Your computer's folders are a tree.

## TreeMap

a Java collection that keeps its keys in sorted order, so you can look up entries and also ask for ranges or the next-larger key.

## Trending topics

the subjects being mentioned most often right now on a platform, computed by counting recent activity.

## Trie (prefix tree)

a tree built from the letters of words, so you can look up everything starting with "ca…" fast. It's what powers autocomplete.

## Two pointers

two markers moving through a list (from both ends, or at different speeds) so you make one pass instead of checking every pair.

## Two-shift scheduling

assigning workers to two work periods (like day and night) while respecting who is available and the rules for each shift.

## Undo/redo

the feature that steps your changes backward and forward, letting you take back a mistake or reapply it.

## Union-find (disjoint set)

keeps track of which items belong to the same group, and merges two groups or checks "same group?" almost instantly.

## uniq command

a Unix command that collapses or filters repeated adjacent lines in text, usually after sorting.

## Unique visitor counts

the number of distinct people who visited a site, counting each person once no matter how many times they came.

## Unix permissions

the settings on Unix and Linux files that control who can read, write, or run each file.

## Uptime monitoring

regularly checking that a website or service is still responding, and alerting someone when it goes down.

## User dictionaries

a personal word list a spellchecker learns from you, so your own names and terms stop being flagged as errors.

## V8 engine

Google's software that runs JavaScript, used inside the Chrome browser and Node.js to execute web and server code fast.

## Vending machines

the coin-and-button machines that dispense snacks or drinks and calculate the change to return.

## Version lookup

finding which version of a file, package, or record applies at a given point, often among many stored versions.

## Version merge

combining two edited versions of the same file into one, keeping both sets of changes where they don't conflict.

## Video editing

assembling and trimming video clips, adding effects and audio, and exporting the finished video.

## Virtual-DOM diffing

comparing a lightweight copy of a web page's structure before and after a change to update only the parts that actually differ.

## WeakMap caches

a JavaScript store that ties cached data to objects and lets it be discarded automatically when those objects are no longer used, so the cache doesn't leak memory.

## Web crawlers

programs that follow links from page to page across the web to collect content, used by search engines to build their index.

## Wire formats

the agreed byte layouts for packaging data so it can be sent between programs or over a network and read back correctly.

## Word puzzle games

games like crosswords or word searches that involve finding, forming, or arranging words.

## XOR checksums

a small check value made by combining all the bytes with XOR, used to catch accidental corruption in stored or transmitted data.

## Zip codes

the postal codes that identify a delivery area, used to sort and route mail and to look up locations.