[leetcode] 110. Balanced Binary Tree 解题报告

题目链接：https://leetcode.com/problems/balanced-binary-tree/

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.

思路：求解一个树是否平衡可以转化为求二叉树的深度，一旦发现左右子树深度相差超过1，则说明不是平衡树。

代码如下：

/**
* 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:
int getDepth(TreeNode* root, bool& flag)
{
//如果当前节点为空则返回深度0，如果flag为false，说明已经判断这不是平衡树，结束程序
if(!root || !flag) return 0;
int dp1 = getDepth(root->left, flag);
int dp2 = getDepth(root->right, flag);
if(abs(dp1 - dp2) > 1) //如果左右子树深度差大于1，说明不是平衡树
flag = false;
return max(dp1, dp2) + 1;
}
bool isBalanced(TreeNode* root) {
if(root == NULL)    return true;
bool flag = true;
getDepth(root, flag);
return flag;
}
};