//Given the root of a binary tree, check whether it is a mirror of itself (i.e., // symmetric around its center). // //

//Given the root of a binary tree, determine if it is a valid binary search tree // (BST). // // A valid BST is defined

//Given the root of a binary tree, return the inorder traversal of its nodes' va //lues. // // // Example 1: // // /

//A message containing letters from A-Z can be encoded into numbers using the fo //llowing mapping: // // //'A' ->

//You are given two integer arrays nums1 and nums2, sorted in non-decreasing ord //er, and two integers m and n, represe

//Given an array of integers heights representing the histogram's bar height whe //re the width of each bar is 1, return

//Given an m x n grid of characters board and a string word, return true if word // exists in the grid. // // The word

//Given an integer array nums of unique elements, return all possible subsets (t //he power set). // // The solution se

//Given two strings s and t of lengths m and n respectively, return the minimum //window substring of s such that every

//Given an array nums with n objects colored red, white, or blue, sort them in-p //lace so that objects of the same colo

//Given an m x n integer matrix matrix, if an element is 0, set its entire row a //nd column to 0's. // // You must do

//You are climbing a staircase. It takes n steps to reach the top. // // Each time you can either climb 1 or 2 steps. I