/** Given a non-empty array of integers nums, every element appears twice except for one. Find that single one. You

/** Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence. You mu

/** A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connec

/** You are given an array prices where prices[i] is the price of a given stock on the iᵗʰ day. You want to maximize

/** Given the root of a binary tree, flatten the tree into a "linked list": The "linked list" should use the same T

/** Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder

Given the root of a binary tree, return its maximum depth. A binary tree’s maximum depth is the number of nodes along th

Given the root of a binary tree, return the level order traversal of its nodes’ values. (i.e., from left to right, level

//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' ->