leetcode刷题， 总结，记录，备忘 110

leetcode110

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.
使用递归，计算每个子树的深度，以及2个子树分别是否为平衡树，这3个条件作为判断条件，还是比较容易理解的。

/**
 * 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 Balanced(TreeNode * root, int & depth)
    {
        if (root == NULL)
        {
            depth = 0;
            return true;
        }
        
        int ldepth, rdepth;
        
        bool left = Balanced(root->left, ldepth);
        bool right = Balanced(root->right, rdepth);
        depth = max(ldepth, rdepth) + 1;
        
        return left && right && abs(ldepth - rdepth) <= 1;
    }
    bool isBalanced(TreeNode* root) {
      int depth;
      return Balanced(root, depth);
    }
};