DSA Practice

Welcome!
This repository is a collection of coding problems organized by Data Structures and Algorithms (DSA) topics. Each problem includes a clear explanation, JavaScript implementation, and notes on which data structure is being used and why.

Whether I’m revisiting core concepts, preparing for upcoming interviews, or just enjoying solving problems — this repo helps me keep everything organized, easy to refer back to, and ready to expand as I go.
Each problem folder includes:

• A clear README.md with the problem statement, approach, and edge cases
• The solution.js file with a working implementation

Categories

Great point — here's an improved version of the table with a note in the "Reference Docs" column indicating that the link points to built-in methods or concept documentation, so it's clear why it's useful before diving into problems:

Category	Path	Reference Docs (In-built Methods / Concepts)
Arrays	arrays/	Array Methods – MDN
Trees	trees/	Tree – GFG (Concept)
Map	map/	Map Methods – MDN
Strings	strings/	String Methods – MDN
Linked Lists	linked-lists/	Linked List – GFG (Concept)
Stacks & Queues	stacks-queues/ (coming soon)	Stack & Queue – GFG (Concept)
Math	basic-math/	Math - MDN

• Learning Resources
  Inside the doc/ folder:
  • Data-Structure1 – Key concepts and when to use what.
  • Code-Compleixty – Time and space complexity tips and cheatsheets.
  • Patterns
  • DSA Cheatsheet

How to Use

• Each folder has a README.md explaining the problem, thought process, and solution.
• How To Run:
  • Directly run any .js file with Node.js to test the solution:
    • Example: node array/easy/001-two-sum/solution.js
  • Run using the central index.js to easily execute problems by their keys:
    • Run the following command with the desired problem key:node index.js ${problemKey} or npm start ${problemKey}
      • You can find the problem key for each problem in the main table.
      • Example: To run the Two Sum solution, use the following command:node index.js twoSum or npm start twoSum

75 Sample Problems (Grouped by Category)

Math / Basic Algorithm

Problem No.	Title	Path/ProblemKey	Difficulty
001	Fizz Buzz	fizzBuzz	Easy
002	Number of Steps to Reduce a Number to Zero	numberOfSteps	Easy
003	Palindrome	palindromeNumber	Easy
004	Roman to Integer	romanToInteger	Easy
005	Plus One	plusOne	Easy (array)
006	Square root	squareRoot	Easy (array, binary search)
007	Fibbonacci Number	fibbonacciNumber	Easy (Dynamic Programming, Recursion, Memoization)
008	Climb stairs	climbStairs	Easy (Dynamic Programming, Memoization)
009	Sum of Digits	sumOfDigits	Easy (Basic Math)
010	Power(x,n)	xRaisedToPowerN	Medium
011	Count Primes	countPrimes	Medium (Sieve of Eratosthenes)
012	Reverse Integer	reverseInteger	Medium
013	Sum of Integer (without + ,-)	sumIntegerWithoutPlusMinus	Medium

Array

Problem No.	Title	Path/Problem Key	Difficulty
001	Two Sum	twoSum	Easy
002	Richest customer wealth	richestCustomerWealth	Easy
003	Sum of 1-D array	sumOf1dArray	Easy
004	Median of Two Sorted Arrays	medianOfTwoSortedArray	Hard
005	Median of Two Sorted Arrays	medianOfTwoSortedArrayMergeSort	Hard
006	Remove Duplicate from sorted arrays	removeDuplicates	Easy (two pointer)
007	Remove Element from array	removeElement	Easy (two pointer)
008	Merge two sorted array	mergeTwoSortedArray	Easy (two pointer, sorting)
009	Pascal Triangle	generatePascalTriangle	Easy (Dynamic Programming)
009	Pascal Triangle II	nthRowOfPascalTriangle	Easy (Dynamic Programming)
010	Best time to sell stock	bestTimeToSellStock	Easy (Dynamic Programming)
011	Two Sum II	twoSumII	Medium (two pointer, binary search)
012	Container With Most Water	containerWithMostWater	Medium (two pointers, greedy)
013	Intersection of two arrays	intersectionOfTwoArrays	Easy
013	Move Zeros	moveZeros	Easy (two pointer)
014	Max Sum Of Sub Array	maxSumOfSubArray	Medium (two pointer)
015	Majority Element	majorityElement	Easy (Hash Table, Divide and Conquer ,Sorting, kadane's Algo)
016	Search in Rotated Sorted Array	searchInRotatedSortedArray	Medium (Binary Search)
017	Peak Index In Mountain Array	peakIndexInMountainArray	Medium (Binary Search)
018	Product except self	productExceptSelf	Medium (Binary Search)
019	Single Element in a Sorted Array	singleNonDuplicate	Medium (Binary Search)
020	Allocate Minimum Pages	allocateMinimumPages	Medium (Searching, Divide and Conquer, Binary Search)
021	Painter's Partition	paintersPartition	Medium (Searching, Divide and Conquer, Binary Search, GFG)
022	Aggressice Cows	aggressiveCows	Medium (Searching, Divide and Conquer, Binary Search, spoj)
023	Sort Colors	sortColors	Medium ( three pointers, leetcode, Dutch National Flag)
024	Next Permutation	nextPermutation	Medium ( two pointers, leetcode)
025	Minimum In Rotated Sorted Array	minimumInRotatedSortedArray	Medium (binary search, leetcode, pivot detection)
026	GCD of Array	gcdOfArray	Easy (leetcode, Math)
027	Row with maximum sum in a Matrix	rowWithMaxSumInMatrix	Easy (gfg, Math)
028	Column with maximum sum in a Matrix	colWithMaxSumInMatrix	Easy (gfg, Math)
029	Matrix Diagonal Sum	matrixDiagonalsSum	Easy (leetcode, Math)
030	Search in 2D matrix	searchIn2dMatrix	Medium (matrix, binary)
031	Search in 2D matrix II	searchIn2dMatrix	Medium (matrix, binary)
032	spiral matrix	spiralMatrix	Medium (matrix, simulation)
032	spiral matrix II	spiralMatrixII	Medium (matrix, simulation)
033	3 Sum	threeSum	Medium (two pointers, sorting)
034	4 Sum	fourSum	Medium (two pointers, sorting)
035	Subsets	subsets	Medium (backtracking)

Map

Problem No.	Title	Path/Problem Key	Difficulty
001	Ransom Note	ransomNote	easy
002	Unique Number of Occurrences	uniqueOccurrences	easy (Set)

String

Problem No.	Title	Path/Problem Key	Difficulty
001	Longest substring without duplicates	longestSubstringNoDuplicate	Medium
002	Longest common prefix	longestCommonPrefix	Easy
003	Find the Index of the First Occurrence in a String	indexOfFirstOccurrence	Easy
004	Length of Last Word	lengthOfLastWord	Easy (Two-pointer)
005	Add Binary	addBinary	Easy (Math, Bit Manipulation, Simulation)
006	Reverse String	reverseString	Easy (Two-pointer)
007	Valid Palindrome	validPalindrome	Easy (Two-pointer)
008	Remove All Occurrences of a Substring	removeOccurrencesOfSubstring	Medium (Stack, Simulation)
009	Permutation in String	permutationInString	Medium (Hash Table, Two Pointers, Sliding Window)
010	Reverse the Words in String	reverseWordsInString	Medium (Two Pointers)
011	String Compression	stringCompression	Medium (Two Pointers, in-place)

Set

Problem No.	Title	Path/Problem Key	Difficulty
001	Longest substring without duplicates	longestSubstringNoDuplicateSet	Medium

Stack

Problem No.	Title	Path/Problem Key	Difficulty
001	Valid Parentheses	validParentheses	Easy
002	132 pattern	OneThreeTwoPattern	Medium, Array, Binary Search, Stack, Monotonic Stack

Tree

Problem No.	Title	Path/Problem Key	Difficulty
001	Root Node Sum Check	rootEqualsSum	Easy

Linked List

Problem No.	Title	Path/Problem Key	Difficulty
001	Middle of linked list	middleNode	Easy
002	Add two numbers	addTwoLinkedListNumber	Medium
003	Merge two sorted List	mergeTwoSortedLinkedList	Easy
004	Delete Duplicates	deleteDuplicates	Easy
005	LinkedList methods	runLinkedListMethods	Easy

Cheatsheet

Work in Progress

This is an evolving repository as I solve more problems.
Feel free to explore, learn, and suggest improvements!

Happy Coding! 🚀