LeetCode OJ - Balanced Binary Tree

题目：

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.

解题思路：

递归求解，注意在求解过程中需要记录左子树和右子树的高度。

代码：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool judge(TreeNode *node, int &depth) {
        if (node == NULL) {
            depth = 0;
            return true;
        }
        
        int left_dep, right_dep;
        bool left_is_balanced = judge(node->left, left_dep);
        bool right_is_balanced = judge(node->right, right_dep);
        
        depth = max(left_dep, right_dep) + 1;
        
        return left_is_balanced && right_is_balanced && (abs(left_dep - right_dep) < 2);
    }
    bool isBalanced(TreeNode *root) {
        int depth = 0;
        return judge(root, depth);
    }
};