Welcome to the 100 Days of Code challenge! Every day, a new coding problem will be posted here. Use this page to track problems, discuss solutions, and improve your problem-solving skills.

📌 How It Works

✅ A new problem will be posted daily.

✅ Every weekend, we will have a discussion session. (online)

✅ Use the group chat to discuss doubts & share solutions!

📢 Join the WhatsApp Discussion Group — click here

📅 Problem Tracker

🏆 Day 🔗 Problem Link 🎯 Difficulty 📂 Topic
Day 1 Add digits 🟢 Easy Math , number theory
Day 2 Count symmetric integers 🟢 Easy math, enumeration
Day 3 Happy Number 🟢 Easy Math , two pointer ,Hash Table
Day 4 Valid perfect square 🟢 Easy Math, Binary search
Day 5 Count total number of colored cells 🟡 medium Math
Day 6 Factorial trailing zeroes 🟡 medium Math
Day 7 Find Sum of Encrypted Integers 🟢 Easy Array , Math
Day 8 https://www.geeksforgeeks.org/problems/gcd-of-two-numbers3459/1 🟢 Easy Math
Day 9 https://leetcode.com/problems/max-consecutive-ones/ 🟢 Easy Array
Day 10 https://leetcode.com/problems/check-if-array-is-sorted-and-rotated/ 🟢 Easy Array
Day 11 https://leetcode.com/problems/two-sum/ 🟢 Easy Array
Day 12 https://leetcode.com/problems/plus-one/ 🟢 Easy Array, Math
Day 13 https://leetcode.com/problems/find-target-indices-after-sorting-array 🟢 Easy Array, Binary Search, Sorting
Day 14 Best time to buy and sell stocks 🟢 Easy Array
Day 15 Set Matrix zeros 🟡 Medium
Array, Hash Table, matrix
Day 16 Max sum of a pair with equal sum of digits 🟡 Medium
Array Hash Table Sorting Heap (Priority Queue)
Day 17 3105. Longest Strictly Increasing or Strictly Decreasing Subarray 🟢 Easy Array
Day 18 Maximum Subarray 🟡 Medium ArrayDivide and ConquerDynamic Programming
Day 19 Binary subarrays with sum 🟡 Medium Array Hash TableSliding WindowPrefix Sum
Day 20 Count number of nice subarrays 🟡 Medium Array
Day 21 https://leetcode.com/problems/product-of-array-except-self/ 🟡 Medium Array, Prefix Sum
Day 22 https://leetcode.com/problems/zero-array-transformation-i 🟡 Medium Array, prefix sum
Day 23 https://leetcode.com/problems/apply-operations-to-an-array 🟡 Medium Array, Two Pointers, Simulation
Day 24 https://leetcode.com/problems/find-peak-element 🟡 Medium Array, Binary search
Day 25 https://leetcode.com/problems/single-element-in-a-sorted-array/ 🟡 Medium Array, Binary search
Day 26 https://leetcode.com/problems/find-the-smallest-divisor-given-a-threshold 🟡 Medium Array, Binary search
Day 27 https://leetcode.com/problems/spiral-matrix/ 🟡 Medium Array
Day 28 https://leetcode.com/problems/length-of-last-word/ 🟢 easy string
Day 29 https://leetcode.com/problems/is-subsequence/ 🟢 easy String , Two Pointers, Dynamic Problem
Day 30 https://leetcode.com/problems/remove-all-occurrences-of-a-substring/description/ 🟡 Medium String
Day 31 https://leetcode.com/problems/reverse-string/ 🟢 easy String , Two Pointers
Day 32 https://leetcode.com/problems/first-unique-character-in-a-string/ 🟢 easy Hash Table
Day 33 https://leetcode.com/problems/jewels-and-stones/ 🟢 easy String , Hash table
Day 34 https://leetcode.com/problems/reverse-words-in-a-string-iii/ 🟢 easy Two Pointers
Day 35 https://leetcode.com/problems/longest-common-prefix/ 🟢 easy String
Day 36 https://leetcode.com/problems/rotate-string/ 🟢 easy String , String Matching
Day 37 https://leetcode.com/problems/isomorphic-strings/description/ 🟢 easy String , Hash Table
Day 38 https://leetcode.com/problems/valid-anagram/ 🟡 Medium String , Hash Table
Day 39 https://leetcode.com/problems/valid-parentheses/description/ 🟢 easy String , Stack
Day 40 https://leetcode.com/problems/reverse-linked-list/ 🟢 easy LinkedList
Day 41 https://leetcode.com/problems/middle-of-the-linked-list/ 🟢 easy LinkedList, two -pointer
Day 41 https://leetcode.com/problems/middle-of-the-linked-list/ 🟢 easy LinkedList, two -pointer
Day 42 https://leetcode.com/problems/linked-list-cycle/ 🟢 easy LinkedList
Day 43 https://leetcode.com/problems/palindrome-linked-list/ 🟡 Medium LinkedList, Two Pointers
Day 44 https://leetcode.com/problems/remove-nth-node-from-end-of-list/ 🟡 Medium LinkedList, Two Pointers
Day 45 https://leetcode.com/problems/remove-duplicates-from-sorted-list 🟢 easy LinkedList
Day 46 https://leetcode.com/problems/remove-linked-list-elements 🟡 Medium LinkedList
Day 47 https://leetcode.com/problems/odd-even-linked-list/ 🟡 Medium Linked List manipulation / reordering
Day 48 https://leetcode.com/problems/single-number/ 🟢 Easy Bit Manipulation, also relates to Hashing and Array
Day 49 https://leetcode.com/problems/number-of-1-bits/ 🟢 Easy Bit Manipulation , Binary Representation
Day 50 https://leetcode.com/problems/power-of-two/ 🟢 Easy Bit Manipulation
Day 51 Missing Number Easy Bit Manipulation, Array, Math
Day 52 Power of three Easy Math Recursion
Day 53 Reverse Bits Easy Bit Manipulation , Divide and conquer
Day 54 Sum of two integers Medium Bit Manipulation
Day 55 implement-stack-using-arrays 🟢 Easy Stack
Day 56 maximum-nesting-depth-of-the-parentheses 🟢 Easy String and Stack
Day 57 min-stack 🟡 Medium Stack and Design
Day 58 final-prices-with-a-special-discount-in-a-shop 🟢 Easy Array and Stack
Day 59 https://leetcode.com/problems/next-greater-element-i/description/ 🟢 Easy Array , Hash table and Stack
Day 60 https://leetcode.com/problems/next-greater-element-ii/description/ 🟡 Medium Array , Stack and Monotonic Stack
Day 61 https://leetcode.com/problems/asteroid-collision/description/ 🟡 Medium Array , Stack and Simulation
Day 62 https://leetcode.com/problems/implement-stack-using-queues/description/ 🟢 Easy Stack and Queue
Day 63 https://leetcode.com/problems/implement-queue-using-stacks/description/ 🟢 Easy Queue and Stacks
Day 64 https://leetcode.com/problems/last-stone-weight/description/ 🟢 Easy Array and Queue
Day 65 https://leetcode.com/problems/kth-largest-element-in-an-array/ 🟢 Easy Array and Queue
Day 66 https://leetcode.com/problems/minimum-operations-to-exceed-threshold-value-ii 🟡 Medium Array, Priority Queue,
Day 67 https://leetcode.com/problems/design-twitter/description/ 🟡 Medium HashTable, LinkedList, Priority Queue
Day 68 https://leetcode.com/problems/merge-k-sorted-lists/description/ Hard LinkedList, MergeSort, PriorityQueue
Day 69 https://leetcode.com/problems/maximum-depth-of-binary-tree Easy Tree, DFS, BFS
Day 70 https://leetcode.com/problems/same-tree Easy Tree, DFS, BFS
Day 71 https://leetcode.com/problems/invert-binary-tree Easy Tree, DFS, BFS
Day 72 https://leetcode.com/problems/minimum-depth-of-binary-tree Easy Tree, DFS, BFS
Day 73 https://leetcode.com/problems/path-sum/description/ Easy Tree, DFS, BFS
day 74 https://leetcode.com/problems/balanced-binary-tree/ Easy Tree, DFS
Day 75 https://leetcode.com/problems/binary-tree-maximum-path-sum/description/ Hard DP, Tree, DFS
Day 76 https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/ Medium ArrayHash TableDivide and ConquerTreeBinary Tree
Day 77 https://leetcode.com/problems/path-sum-ii/description/ Medium Tree, DFS, BFS
Day 78 https://leetcode.com/problems/path-sum-ii/description/ Medium Backtracking, Tree, DFS
Day 79 http://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/ Medium Tree, DFS, BFS
Day 80 https://leetcode.com/problems/flood-fill/description/ Easy Array, DFS, BFS, Matrix
day 81 https://leetcode.com/problems/number-of-provinces/description/ Medium DFS, BFS, graph
Day 82 https://leetcode.com/problems/rotting-oranges/description/ Medium Array, BFS, Matrix
Day 83 https://leetcode.com/problems/number-of-islands/ Medium Array, DFS, BFS, Matrix
Day 84 https://leetcode.com/problems/find-the-town-judge Easy Array, HashTable, Graph

📚 Resources 📖

📌 LeetCode

📌 GeeksforGeeks

📌 Code forces

💡 Stay consistent, keep coding, and let’s grow together! 🚀🔥