Data Structures and Algorithms

May 6, 2026 · View on GitHub

A comprehensive collection of data structures and algorithms implemented in multiple programming languages. This repository serves as a resource for learning and practicing fundamental computer science concepts.

Overview

This repository contains implementations of various data structures and algorithms, organized by category. Each implementation includes:

Source code
Interactive playground (where available)
Documentation explaining the concept, approach, and complexity

The implementations are primarily in JavaScript, with some examples in other languages like Java, TypeScript, and Go.

Data Structures

Stack

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Stack using array	Source	JavaScript	-	Easy	Using Array operations	Use array push/pop for stack behavior
2	Stack using linkedlist	Source	JavaScript	-	Easy	Using LinkedList operations	Use linked list nodes for stack push/pop

Queue

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Queue using array	Source	JavaScript	Documentation	Easy	Using Array operations	Use array shift/unshift or circular buffer
2	Queue using linkedlist	Source	JavaScript	Documentation	Easy	Using LinkedList operations	Maintain head/tail pointers for enqueue/dequeue

SinglyLinkedList

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	SinglyLinkedList implementation	Source	JavaScript	Documentation	Easy	Linked List operations	Use nodes with next pointer for insert/delete

DoublyLinkedList

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	DoublyLinkedList implementation	Source	JavaScript	Documentation	Easy	Linked List operations	Use nodes with prev/next pointers for insert/delete

Tree

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Binary Search Tree	Source	JavaScript	Documentation	Medium	Tree operations	Use left/right pointers, recursive insert/search

Graphs

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Unweighted undirected graph	Source	JavaScript	Documentation	Medium	Graph operations	Use adjacency list/matrix for traversal

HashTable

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	HashTable	Source	JavaScript	-	Medium	Hash operations	Use hash function for key-value storage

Algorithms

Array

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Contains duplicates	Source	Playground	Documentation	Easy	Set/Object	Verify duplicate using set or map/dict/object
2	Two sum2- Input array sorted	Source	Playground	Documentation	Medium	Two pointers	Use left/right pointers to find target sum
3	3 sum	Source	Playground	Documentation	Medium	Two pointers	Sort, fix one element, use two pointers for others
4	Product of array except self	Source	Playground	Documentation	Medium	Prefix and postfix pattern	Compute left and right products for each index
5	Max sum subarray	Source	Playground	Documentation	Medium	Kadane's algorithm	Track max sum ending at each index
6	Minimum size subarray sum	Source	Playground	Documentation	Medium	Sliding window	Expand/shrink window to meet sum
7	Sort Colors	Source	Playground	Documentation	Medium	Two pointers	Dutch National Flag: 3-way partition
8	Maximum product subarray	Source	Playground	Documentation	Medium	Kadane's algorithm	Track max/min products at each index
9	Find minimum in rotated sorted array	Source	Playground	Documentation	Medium	Binary search technique	Use binary search to find inflection point
10	Maximum Circular subarray	Source	Playground	Documentation	Medium	Kadane's algorithm	Max of normal and circular subarray sum
11	Rotate array	Source	Playground	Documentation	Medium	Two pointers	Reverse parts and whole array
12	Search in rotated sorted array	Source	Playground	Documentation	Medium	Binary search	Modified binary search for rotation
13	Container with most water	Source	Playground	Documentation	Medium	Two pointers	Calculate max area and move shorter pointer inward
14	First missing positive number	Source	JavaScript	Documentation	Hard	In-place hashing	Place numbers at correct indices
15	Best time to buy stock and sell stock	Source	JavaScript	Documentation	Easy	Greedy algorithm	Look for minprice at each position
16	Two missing numbers	Source	JavaScript	Documentation	Medium	Sum and average calculations	Use sum and sum of squares to find missing
17	Pascal's Triangle	Source	JavaScript	Documentation	Easy	Array traversal and sequential sum	Build each row using previous row
18	Remove Element	Source	JavaScript	Documentation	Easy	Array traversal	Overwrite target elements in-place
19	Can place flowers	Source	JavaScript	Documentation	Easy	Array traversal and comparison	Check adjacent plots for placement
20	Majority Element	Source	JavaScript	Documentation	Easy	Boyer Moore Voting algorithm	Track candidate and count
21	Pivot Index	Source	JavaScript	Documentation	Easy	Array traversal	Compare left/right sums at each index
22	Range Sum queries	Source	JavaScript	Documentation	Easy	Array traversal	Precompute prefix sums for fast queries
23	Disappeared numbers	Source	JavaScript	Documentation	Easy	Array traversal	Mark visited indices, collect missing
24	Identical pairs	Source	JavaScript	Documentation	Easy	Array traversal & map	Count occurrences, use nC2 formula
25	Destination City	Source	JavaScript	Documentation	Easy	Array traversal & set	Find city with no outgoing path
26	Set mismatch	Source	JavaScript	Documentation	Easy	Array traversal & marking numbers	Find duplicate and missing
27	Intersection of arrays	Source	JavaScript	Documentation	Easy	Set and array traversal	Use sets for intersection
29	Special array	Source	JavaScript	Documentation	Easy	Frequency counter and array traversal	Check for special property by counting frequencies
30	Max length between equal chars	Source	JavaScript	Documentation	Easy	Array traversal	Store first/last index of each char
31	Third largest element	Source	JavaScript	Documentation	Easy	Array traversal	Track top 3 elements
32	Odd occurrences	Source	JavaScript	Documentation	Easy	XOR operation	XOR all elements to find odd occurrence
33	Max counters	Source	JavaScript	Documentation	Medium	Lazy update strategy	Use lazy update to avoid repeated operations
34	Tape equilibrium	Source	JavaScript	Documentation	Easy	Prefix sum	Track left/right sums, find min difference
35	Perm check	Source	JavaScript	Documentation	Easy	Set operations	Check if all numbers from 1 to N are present
36	Equi leader	Source	JavaScript	Documentation	Medium	Boyer-Moore algorithm	-
37	Count triangles	Source	JavaScript	Documentation	Medium	Two pointers	-
38	Min abs sum of two	Source	JavaScript	Documentation	Medium	Two pointers	-
39	Abs distinct	Source	JavaScript	Documentation	Easy	Two pointers	-
40	Count distinct slices	Source	JavaScript	Documentation	Medium	Sliding window	-

String

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Longest substring without repeating characters	Source	JavaScript	Documentation	Medium	Sliding Window	set to remove duplicates or map/dict with (char,index) key-value pairs to jump position
2	Longest repeating character replacement	Source	JavaScript	Documentation	Medium	Sliding Window	char frequency dict/map/array with windowLength-maxFrequency > k check
3	Minimum window substring	Source	JavaScript	Documentation	Hard	Sliding Window	Two char frequecies map/dict for finding minimum length based on having == required
4	Valid anagram	Source	JavaScript	Documentation	Easy	Frequency counting	Balancing char frequency list
5	Group anagrams	Source	JavaScript	Documentation	Medium	Frequency counting	Group anagrams based on unique key(counter or sorted)
6	Valid palindrome	Source	JavaScript	Documentation	Easy	Two pointer	Compare two strings using two pointers
7	Longest palindromic substring	Source	JavaScript	Documentation	Medium	Expanding around center	-
8	Palindromic substrings	Source	JavaScript	Documentation	Medium	Expanding around center	-
9	Encode and decode strings	Source	JavaScript	Documentation	Medium	Basic string and array operations	-
10	Greatest common devisor of strings	Source	JavaScript	Documentation	Easy	Euclidean and String operations	-
11	Reverse words in string	Source	JavaScript	Documentation	Medium	Basic string and array operations	-
12	Length of last word	Source	JavaScript	Documentation	Easy	String traversal	-

Dynamic programming

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Climbing stairs	Source	JavaScript	Documentation	Medium	Dynamic programming	Use DP to build up the number of ways to reach each step from previous two steps.
2	Coin change	Source	JavaScript	Documentation	Medium	Dynamic programming	For each amount, try every coin and use DP to find the minimum coins needed.
3	Longest increasing subsequence	Source	JavaScript	Documentation	Medium	Dynamic programming (Bottom up)	For each element, find the longest increasing subsequence ending at that element.
4	Longest common subsequence	Source	JavaScript	Documentation	Medium	Two-dimentional bottom up Dynamic programming	Use a DP table to track the longest subsequence for all prefixes of both strings.
5	Word break	Source	JavaScript	Source	Medium	Bottom up dynamic programming	For each index, check if any word in the dictionary ends there and the prefix is breakable.
6	Combination Sum 4	Source	JavaScript	Documentation	Medium	Bottom up Dynamic programming	For each total, sum the ways to reach it using all numbers in the array.
7	House robber	Source	JavaScript	Documentation	Medium	Fibonacci pattern bottom-up dynamic programming	At each house, choose max of robbing it plus two houses back or skipping it.
8	House robber 2	Source	JavaScript	Documentation	Medium	Bottom-up dynamic programming	Like House Robber, but first and last houses are adjacent, so solve twice (excluding each end).
9	Decode ways	Source	JavaScript	Documentation	Medium	Dynamic programming	For each position, sum the ways to decode one or two digits if valid.
10	Unique paths	Source	JavaScript	Documentation	Medium	Dynamic programming	Use DP to count ways to reach each cell from top or left.
11	Jump game	Source	JavaScript	Documentation	Medium	Dynamic programming or Greedy	Track the farthest index you can reach at each step.
12	Min abs sum	Source	JavaScript	Documentation	Medium	Dynamic programming	Use DP to partition numbers into two groups with minimal absolute difference.
13	Number solitaire	Source	JavaScript	Documentation	Medium	Dynamic programming	At each cell, choose the best score from the previous 6 cells plus current value.

Binary

No.	Name	Source	Playground	Documentation	Level	Pattern	Hint
1	Sum of two integers	Source	JavaScript	Documentation	Medium	Bitwise operations	Use bitwise operations to add without using '+'.
2	Number of 1 Bits	Source	JavaScript	Documentation	Easy	Brian Kernighans	Repeatedly clear the lowest set bit using n & (n-1).
3	Counting Bits	Source	JavaScript	Documentation	Easy	Dynamic programming	For each number, count bits as 1 + bits in n & (n-1).
4	Missing number	Source	JavaScript	Documentation	Easy	Bitwise XOR	-
5	Reverse Bits	Source	JavaScript	Documentation	Easy	Bitwise operations	-

Stack

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Sort Stack	Source	JavaScript	Documentation	Easy	Stack push & pop	Use an auxiliary stack to insert elements in sorted order.
2	Balanced Brackets	Source	JavaScript	Documentation	Medium	Stack push and pop	Push opening brackets, pop and check for matching closing brackets.
3	Reverse Polish Notation	Source	JavaScript	Documentation	Medium	Stack push & pop	Push operands, pop two for each operator, compute and push result.
4	Daily Temperatures	Source	JavaScript	Documentation	Medium	Monotonic decreasing stack	Use stack to keep indices, pop when a warmer day is found.
5	Number of People See In Queue	Source	JavaScript	Documentation	Medium	Monotonic decreasing stack	Use stack to count visible people for each position.

LinkedList

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Reverse sublist	Source	JavaScript	Documentation	Easy	List traversal	Reverse pointers between left and right positions.
2	Detect cycle in a linkedlist	Source	JavaScript	Documentation	Easy	Floyd's cycle-finding algorithm	Use slow and fast pointers to detect a cycle.
3	Merge two sorted lists	Source	JavaScript	Documentation	Easy	Arithmetic comparison	Compare heads, attach smaller node, repeat.
4	Merge K sorted lists	Source	JavaScript	Documentation	Hard	Divide and conquer	Merge pairs of lists recursively or use a min-heap.
5	Remove Kth node from end of list	Source	JavaScript	Documentation	Medium	Two pointers	-
6	Reorder list	Source	JavaScript	Documentation	Medium	Two pointers	-
7	Find middle node	Source	JavaScript	Documentation	Easy	Two pointers	-
8	Find Kth node from end of list	Source	JavaScript	Documentation	Easy	Two pointers	-
9	Partition list	Source	JavaScript	Documentation	Medium	Two pointers	-
10	Remove duplicates	Source	JavaScript	Documentation	Easy	Two pointers	-
11	Binary to decimal	Source	JavaScript	Documentation	Easy	List traversal and math operations	-

DoublyLinkedList

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Swap first and last	Source	JavaScript	Documentation	Easy	Swap nodes	Swap head and tail node values.
2	Palindrome check	Source	JavaScript	Documentation	Easy	Two pointers	-
3	Swap node pairs	Source	JavaScript	Documentation	Medium	List traversal and pointer updates	-

Tree

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Maximum depth of binary tree	Source	JavaScript	Documentation	Easy	DFS with recursion	Recursively find max depth of left and right subtrees.
2	Same tree	Source	JavaScript	Documentation	Easy	DFS with recursion	Recursively compare values and subtrees of both trees.
3	Invert or Flip binary tree	Source	JavaScript	Documentation	Easy	DFS with recursion	Recursively swap left and right children of each node.
4	Binary tree maximum path sum	Source	JavaScript	Documentation	Hard	DFS using recursion	At each node, compute max path sum including or excluding the node.
5	Binary tree level order traversal	Source	JavaScript	Documentation	Easy	BFS traversal	Use a queue to traverse nodes level by level.
6	Serialize and deserialize binary tree	Source	JavaScript	Documentation	Hard	DFS preorder traversal	-
7	Subtree of another tree	Source	JavaScript	Documentation	Easy	DFS with recursion	-
8	Construct binary tree from traversals	Source	JavaScript	Documentation	Medium	DFS with recursion	-
9	Validate BST	Source	JavaScript	Documentation	Medium	DFS using recursion	-
10	Kth smallest element in BST	Source	JavaScript	Documentation	Medium	Inorder traversal	-
11	Lowest Common Ancestor of BST	Source	JavaScript	Documentation	Medium	Tree traversal	-
12	Trie	Source	JavaScript	Documentation	Medium	String character iteration	-
13	Design and Search words Datastructure	Source	JavaScript	Documentation	Medium	Trie and DFS recursion	-
14	Word search 2	Source	JavaScript	Documentation	Hard	Backtracking with Trie	-

Graph

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Clone graph	Source	JavaScript	Documentation	Medium	DFS using recursion	-
2	Course schedule	Source	JavaScript	Documentation	Medium	DFS using recursion	-
3	Pacific Atlantic waterflow	Source	JavaScript	Documentation	Medium	DFS using recursion	-
4	Number of Islands	Source	JavaScript	Documentation	Medium	DFS using recursion	-
5	Alien dictionary	Source	JavaScript	Documentation	Hard	Topological sorting	-
6	Graph valid tree	Source	JavaScript	Documentation	Medium	Union Find algorithm	-
7	Number of connected components	Source	JavaScript	Documentation	Medium	Union Find algorithm	-
8	Walls and gates	Source	JavaScript	Documentation	Medium	BFS traversal	-
9	Fib frog	Source	JavaScript	Documentation	Medium	Dynamic programming	-

Matrix

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Set matrix zeros	Source	JavaScript	Documentation	Medium	In-place updates	-
2	Spiral matrix	Source	JavaScript	Documentation	Medium	Boundary traversal	-
3	Rotate image	Source	JavaScript	Documentation	Medium	In-place rotation	-
4	Word search	Source	JavaScript	Documentation	Medium	DFS using recursion	-

Interval

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Insert interval	Source	JavaScript	Documentation	Medium	Math operations	-
2	Merge interval	Source	JavaScript	Documentation	Medium	Sorting and math operations	-
3	Non-overlapping intervals	Source	JavaScript	Documentation	Medium	Greedy algorithm	-
4	Meeting rooms	Source	JavaScript	Documentation	Medium	Greedy algorithm	-
5	Meeting rooms 2	Source	JavaScript	Documentation	Medium	Two pointers	-
6	Meeting rooms 3	Source	JavaScript	Documentation	Medium	Greedy algorithm	Two minheaps + greedy scheduling + simulation
7	Max non-overlapping segments	Source	JavaScript	Documentation	Medium	Greedy algorithm	-

HashTable

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Duplicates	Source	JavaScript	Documentation	Easy	Using Map	-
2	Two sum	Source	JavaScript	Documentation	Easy	Using Map	-
3	First non repeating character	Source	JavaScript	Documentation	Easy	Using Map	-
4	Group anagrams	Source	JavaScript	Documentation	Medium	Map methods	-
5	Verify Common Elements	Source	JavaScript	Documentation	Easy	Map methods	-
6	Longest consecutive sequence	Source	JavaScript	Documentation	Medium	Set operations	-
7	Valid Sudoku	Source	JavaScript	Documentation	Medium	Map and Set methods	-
8	Letter combinations	Source	JavaScript	Documentation	Medium	Backtracking with hash mapping	-
9	LRU Cache	Source	JavaScript	Documentation	Medium	Hash Table with linked list	-
10	Maximum number of balloons	Source	JavaScript	Documentation	Easy	Character frequency map	-
11	Isomorphic Strings	Source	JavaScript	Documentation	Easy	Character mapping	-
14	First unique character	Source	JavaScript	Documentation	Easy	Character frequency count	-

Sorting

No.	Name	Source	Live	Documentation	Level	Complexity	Hint
1	Bubble sort	Source	JavaScript	Documentation	Easy	TC: O(n²), SC: O(1)	-
2	Selection sort	Source	JavaScript	Documentation	Easy	TC: O(n²), SC: O(1)	-
3	Insertion sort	Source	JavaScript	Documentation	Easy	TC: O(n²), SC: O(1)	-
4	Merge sort	Source	JavaScript	Documentation	Medium	TC: O(n log n), SC: O(n)	-
5	Quick sort	Source	JavaScript	Documentation	Medium	TC: O(n²), SC: O(log n)	-
6	Heap sort	Source	JavaScript	Documentation	Hard	TC: O(n log n), SC: O(1)	-
7	Radix sort	Source	JavaScript	Documentation	Medium	TC: O(d(n+k)), SC: O(n+k)	-
8	Max product of three	Source	JavaScript	Documentation	Easy	Array sorting	-

Misc

No.	Name	Source	Live	Documentation	Level	Pattern	Hint
1	Frog jump	Source	JavaScript	Documentation	Easy	Mathematical calculation	-
2	Missing element	Source	JavaScript	Documentation	Easy	Mathematical calculation	-
3	Frog river one	Source	JavaScript	Documentation	Easy	Set operations	-
4	Count divisible	Source	JavaScript	Documentation	Easy	Mathematical calculation	-