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Algorithm Visualizer

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Learning ToolsAlgorithm Complexity ReferenceAlgorithm Learning Paths
Data StructuresArrayLinked ListStackQueue and DequeBinary Search TreeBinary HeapHash TableGraphTrieDisjoint Set UnionLRU CacheSkip ListSegment TreeB+ TreeBloom FilterFenwick Tree
SortingBubble SortCocktail Shaker SortBitonic SortSelection SortInsertion SortBinary Insertion SortShell SortMerge SortTop-Down Merge SortQuick SortThree-Way Quick SortDual-Pivot Quick SortHeap SortCounting SortRadix SortBucket Sort
Graph AlgorithmsDijkstra's Shortest PathKruskal's Minimum Spanning TreePrim's Minimum Spanning TreeBellman-Ford Shortest PathsTopological SortFloyd-WarshallStrongly Connected Components2-SATMaximum FlowBipartite MatchingLowest Common AncestorEulerian Path
Dynamic ProgrammingEdit Distance0/1 KnapsackUnbounded KnapsackLongest Common SubsequenceLongest Increasing SubsequenceCoin ChangeStone MergingTraveling Salesperson DPTree Dynamic ProgrammingDigit DPRerooting DP
Backtracking and SearchN-QueensSubsetsPermutationsCombination SumMaze Solving with DFSNumber of IslandsWord SearchSudoku SolverA* Search
StringsKMP String MatchingRabin-Karp String MatchingBoyer-Moore String MatchingManacher's Longest Palindromic SubstringSuffix ArrayLCP ArrayAho-Corasick AutomatonZ Function
Math and Number TheorySieve of EratosthenesLinear SieveEuclidean AlgorithmBinary ExponentiationExtended Euclidean AlgorithmChinese Remainder TheoremEuler's Totient FunctionMiller-Rabin Primality TestFast Fourier TransformPollard's Rho Factorization
Computational GeometryConvex HullRotating CalipersClosest Pair of PointsLine Segment IntersectionBentley-Ottmann Sweep Line
SearchingBinary SearchLower and Upper BoundSearch in a Rotated Sorted ArrayBinary Search on the AnswerTernary Search

Stack

Last in, first out through one active end

Only the top is exposed

A stack accepts push and pop at the same end. The newest value is therefore the first one removed, a rule known as last in, first out (LIFO). peek reads that value without changing the stack.

Try it
Stack is empty

Press push to add an item.

An array-backed stack keeps the top at the end of a dynamic array, so push and pop are amortized O(1). A linked implementation can make both operations worst-case O(1) by treating the list head as the top.

Why stacks appear in algorithms

Function calls use a stack to remember return points and local state. Depth-first search uses the same idea explicitly or through recursion. Parsers, expression evaluators, undo history, and monotonic-stack algorithms all rely on controlled access to the most recent unfinished item.

Invariant: every pop removes exactly the value returned by the most recent unmatched push.

Compare LIFO ordering with the first-in, first-out behavior of a queue.