leetcode之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.

解答：

对于每个节点求其子树深度然后判断是否是height-balanced即可

/**
 * 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 depth(TreeNode* root)
    {
        if(root == NULL)
            return 0;
        int l = depth(root->left);
        int r = depth(root->right);
        return l > r? l + 1 : r + 1;
    }
    bool isBalanced(TreeNode* root) {
      if(root == NULL)
        return true;
      int l = depth(root->left);
      int r = depth(root->right);
      if(abs(l - r) > 1)
        return false;
      return isBalanced(root->left) && isBalanced(root->right);
    }
};