Algorithms Strings Problems Valid Palindrome source leetcode Arrays Prerequisites Reverse Problems Two Sum source leetcode Best time to buy and sell stock source leetcode Binary Search source leetcode Linked Lists Prerequisites Singly Linked List Doubly Linked List Singly Circular Linked List Reverse Singly Linked List Cycle Detection Problems Merge two sorted lists source leetcode Stack Prerequisites Stack Problems Valid Parantheses source leetcode Graph Prerequisites Graph Matrix/Grid Prerequisites 2D Matrix Problems Flood Fill - source - leetcode Island Perimeter - source - leetcode