Data structures and algorithms, explained in plain English.

Binary search is an efficient algorithm for finding a target value in a sorted array.

Sorting algorithms rearrange a collection into a defined order, usually ascending.

Two pointers is an algorithmic pattern that uses two indices to traverse a data structure, usually an array or string, instead of one.

The sliding window is an algorithm pattern that maintains a moving sub-range over a linear structure like an array or string.

Dynamic programming is an algorithmic technique that solves a complex problem by breaking it into overlapping subproblems, solving each one only once, and storing the result to reuse later.

Backtracking is a general technique for solving problems by building a solution one choice at a time and abandoning a partial solution the moment it cannot lead to a valid answer.

A greedy algorithm builds a solution step by step, always taking the choice that looks best right now, the locally optimal option, and never undoing it.

Recursion is when a function solves a problem by calling itself on a smaller version of that problem.

Big O notation is a way to describe how an algorithm's running time or memory use grows as its input gets larger.

A hash table is a data structure that stores key-value pairs and finds any value in O(1) time on average.

An array is a collection of elements stored side by side in contiguous memory, each reachable by a numeric index.

A linked list is a linear data structure where each element, called a node, stores a value and a pointer (reference) to the next node.

A stack is a linear data structure that stores items in last-in, first-out (LIFO) order: the most recently added element is the first one removed.

A queue is a linear data structure that stores items in first-in, first-out (FIFO) order: you add elements at the back (enqueue) and remove them from the front (dequeue).

A binary tree is a hierarchical data structure made of nodes, where each node holds a value and links to at most two children, called left and right.

A heap is a complete binary tree that satisfies the heap property: in a min-heap every parent is smaller than or equal to its children, so the minimum sits at the root (a max-heap flips this).

A graph is a data structure that models relationships as a set of vertices (nodes) connected by edges (links).

A trie, or prefix tree, stores strings by their characters: every node is one character and every word is a path from the root.

Union-Find, also called disjoint set union (DSU), keeps track of which items belong to the same group while groups keep merging.

Breadth-first search (BFS) is a graph traversal algorithm that explores a graph level by level, visiting all neighbors of a node before moving deeper.

Depth-first search (DFS) is a graph and tree traversal algorithm that explores as far as possible along each branch before backtracking.

A topological sort puts the nodes of a directed acyclic graph in an order where every edge points forward: if A must happen before B, A comes first.

Bit manipulation is the technique of operating directly on the individual binary digits of integers using bitwise operators, AND, OR, XOR, NOT, and left/right shifts.