LeetCodeChallenges Problems Two Sum Add Two Numbers Longest Substring Without Repeating Characters ALGORITHM Challenges Binary Search LeetCode 75 Level 1 Day 1 - Prefix Sum : Running Sum of 1d Array Find Pivot Index Day 2 - String : Isomorphic Strings Is Subsequence Day 3 - Linked List : Merge Two Sorted Lists Reverse Linked List Day 4 - Linked list : Middle of the Linked List Linked List Cycle II Day 5 - Greedy : Best Time to Buy and Sell Stock Longest Palindrome Day 6 - Tree : N-ary Tree Preorder Traversal Binary Tree Level Order Traversal Day 7 - Binary Search : Binary Search First Bad Version Day 8 - Binary Search Tree : Validate Binary Search Tree Lowest Common Ancestor of a Binary Search Tree Day 9 - Graph/BFS/DFS : Flood Fill Number of Islands Day 10 - Dynamic Programming : Fibonacci Number Climbing Stairs Day 11 - Dynamic Programming : Min Cost Climbing Stairs Unique Paths Day 12 - Sliding Window/Two Pointer : Find All Anagrams in a String Longest Repeating Character Replacement Day 13 - Hashmap : Two Sum Bulls and Cows Day 14 - Stack : Backspace String Compare Decode String Day 15 - Heap : Last Stone Weight Top K Frequent Words