LeetCode-110. Balanced Binary Tree

问题：https://leetcode.com/problems/balanced-binary-tree/?tab=Description
Given a binary tree, determine if it is height-balanced. 判断二叉树是否为平衡二叉树。
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. 树上的任意结点的左右子树高度差不超过1，则为平衡二叉树。
分析：计算左右树的高度，高度差不能大于1 。
参考C++代码：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isBalanced(TreeNode* root) {        if(root==NULL) return true;        if(root->left==NULL && NULL==root->right) return true;        if((getHeight(root->left)-getHeight(root->right)>1) || (getHeight(root->right)-getHeight(root->left)>1)) return false;        return isBalanced(root->left) && isBalanced(root->right);    }    int getHeight(TreeNode *root){        if(NULL==root) return 0;        if(NULL==root->right && NULL==root->left) return 1;        int lH=getHeight(root->left);        int rH=getHeight(root->right);        return lH>rH?lH+1:rH+1;    }};