[leetcode] 110. Balanced Binary Tree 解題報告

題目連結：https://leetcode.com/problems/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.

思路：求解一個樹是否平衡可以轉化為求二叉樹的深度，一旦發現左右子樹深度相差超過1，則說明不是平衡樹。

代碼如下：

/**
 * 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 height(TreeNode* root) 
    {
        if(!root) return 0;
        int left = height(root->left);
        if(left==-1) return -1;
        int right = height(root->right);
        if(right==-1) return -1;
        if(abs(left-right)>1) return -1;
        return max(left, right)+1;
    }
    
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        return height(root)==-1?false:true;
    }
};