问题描述：
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 differ by more than 1.
判断一个二叉树是否是二叉平衡树，即左右子树高度差不超过一。在之前的求二叉树的深度的基础上（代码见二叉树深度）
遍历每个节点，求其左右子树的深度，然后看深度差是不是小于等于1即可。
AC代码如下：
int TreeDepth(TreeNode * root) { if(root == NULL) return 0; int left = TreeDepth(root->left); int right = TreeDepth(root->right); return (left>right?left+1:right+1); } bool isBalanced(TreeNode* root) { if(root == NULL) return true; int left = TreeDepth(root->left); int right = TreeDepth(root->right); int diff = abs(left-right); if(diff > 1) return false; return isBalanced(root->left) && isBalanced(root->right); }