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.
✅ 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
| 🏆 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 |
| Day 85 | https://leetcode.com/problems/find-if-path-exists-in-graph/ | 🟢 Easy | Depth-First Search, Breadth-First Search, Union Find and Graph |
| Day 86 | https://leetcode.com/problems/01-matrix/ | 🟡 Medium | Array, Dynamic Programming, Breadth-First Search and Matrix |
| Day 87 | https://leetcode.com/problems/shortest-path-in-binary-matrix/ | 🟡 Medium | Array, Breadth-First Search and Matrix |
| Day 88 | https://leetcode.com/problems/cheapest-flights-within-k-stops/description/ | 🟡 Medium | DFS, BFS, DP, PriorityQueue |
| Day 89 | https://leetcode.com/problems/number-of-operations-to-make-network-connected/ | 🟡 Medium | DFS, BFS, graph |
| Day 90 | https://leetcode.com/problems/course-schedule/description/ | 🟡 Medium | DFS, BFS, graph, Topo Sort |
| Day 91 | https://leetcode.com/problems/climbing-stairs/ | Easy | DP, memoization |
| Day 92 | https://leetcode.com/problems/house-robber/description/ | Medium | Array, DP |
| Day 93 | https://leetcode.com/problems/house-robber-ii/description/ | Medium | Array, DP |
| Day 94 | https://leetcode.com/problems/unique-paths/ | 🟡 Medium | Math, DP and Combinatorics |
| Day 95 | https://leetcode.com/problems/minimum-path-sum/ | 🟡 Medium | Math, DP and Matrix |
| Day 96 | https://leetcode.com/problems/minimum-falling-path-sum/ | 🟡 Medium | Math, DP and Matrix |
| Day 97 | https://leetcode.com/problems/partition-equal-subset-sum/ | 🟡 Medium | Array and DP |
| Day 98 | https://leetcode.com/problems/assign-cookies/ | 🟢 Easy | Array, Two Pointers, Greedy and Sorting |
📌 LeetCode
💡 Stay consistent, keep coding, and let’s grow together! 🚀🔥