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Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the f

题目链接在此 Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 基于一个有序数组，建立BST。 直观的做法：取数组中点作为根，左侧数组作为左子树，右侧数组作为右子树，不断递归地建树。 class Solution { publ

这是两道题。 98. Validate Binary Search Tree 99. Recover Binary Search Tree 98题：判断一棵树是不是合法的二叉搜索树（BST）。 BST有个可以用脚后跟想出来的特点：中序遍历可以得到一个递增的序列。那我们就中序遍历，看看他是不是严格递增 就可以了。 那么怎样做到不开辟新的空间呢？用一个last

这是两道题： 102. Binary Tree Level Order Traversal 103. Binary Tree Zigzag Level Order Traversal 102这道题就是按层次遍历，但是要把每一层的节点分别存储到vector里面去。 两年前就做过这道题，还写了博客。 当时的做法是硬生生地给每个结点加了个域，用来标记高度。很蹩脚。 今天做10

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20

题目链接在此 Given a binary tree, flatten it to a linked list in-place. For example, Given 1 / \ 2 5 / \ \ 3 4 6 The flattened tree should look lik

题目链接在此 Given a set of distinct integers, nums, return all possible subsets. Note: Elements in a subset must be in non-descending order.The solution set must not contain duplicate subs

题目链接在此 Given a binary search tree, write a function kthSmallest to find the kth smallest element in it. Note:  You may assume k is always valid, 1 ≤ k ≤ BST's total elements. Follow

题目链接在此 Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is de

Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never diffe

题目链接在此 Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Fin