#93 Balanced Binary Tree

题目描述：

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.

Have you met this question in a real interview? 

Yes

Example

Given binary tree A = {3,9,20,#,#,15,7}, B = {3,#,20,15,7}

A)  3            B)    3    / \                  \  9  20                 20    /  \                / \   15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.

题目思路：

这题就用recursion做，然后我还算了每个node的height，返回true的条件是height之差小于等于1并且左子树和右子树都balance。

Mycode（AC = 13ms）：

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */class Solution {public:    /**     * @param root: The root of binary tree.     * @return: True if this Binary tree is Balanced, or false.     */    bool isBalanced(TreeNode *root) {        // write your code here        if (root == NULL) {            return true;        }                return abs(height(root->left) - height(root->right)) <= 1 &&               isBalanced(root->left) && isBalanced(root->right);    }        int height(TreeNode *root) {        if (root == NULL) {            return 0;        }                return max(height(root->left), height(root->right)) + 1;    }};