Today, we are working on 125. Valid Palindrome A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s, return true if it is a…

Today, we are working on 124. Binary Tree Maximum Path Sum A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the…

Today, we are working on 121. Best Time to Buy and Sell Stock You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a…

Today, we are working on 105. Construct Binary Tree from Preorder and Inorder Traversal Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

Today, we are working on 104. Maximum Depth of Binary Tree Given the root of a binary tree, return its maximum depth. A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Today, we are working on 102. Binary Tree Level Order Traversal. Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).

Today, we are going to work on 100. Same Tree Given the roots of two binary trees p and q, write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical, and the nodes have the same…

We have gone through the first third of the blind 75 list. It’s a good time to review what we’ve done so far and techniques we’ve used. We also want to see if we can identify any relationship between type of problem and techniques we can use. Referring back to…

Today, we are working on 98. Validate Binary Search Tree Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node’s key. …