LeetCode 110. 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.

这个题目的意思是，如果一个二叉树树的任何节点的左右子树的深度之差不大于1，就是一个高度平衡的二叉树，求你判断一棵树是否是高度平衡的二叉树

我的思路是，如果遍历到某个节点时，它的左右子树深度之差大于1，则返回-1，否则返回以这个节点为跟时树的高度，这样遍历完全后，即可判断是否是平衡的二叉树

 

/**
 * 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 depthFirstSearch(TreeNode *root)
	{
		if (root == NULL)return 0;
		int leftdep = depthFirstSearch(root->left);
		int rightdep=depthFirstSearch(root->right);
		if (abs(leftdep - rightdep) > 1|| leftdep == -1 || rightdep == -1)return -1;
		return leftdep > rightdep ? leftdep + 1 : rightdep + 1;
	}
	bool isBalanced(TreeNode* root) {
		if (depthFirstSearch(root) == -1)return false;
		else return true;
	}
};