【LeetCode110】Balanced Binary Tree

/**
 * 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* node){
        if(node == NULL)
            return 0;
        int left = height(node->left);
        if(left == -1)
            return -1;
        int right = height(node->right);
        if(right == -1)
            return -1;
        if(abs(left-right)>1)
            return -1;
        else
            return max(left, right)+1;
    }

    bool isBalanced(TreeNode* root) {//左右子树是平衡二叉树，且高度差不超过1
        int result = height(root);
        if(result == -1)
            return false;
        else
            return true;
    }
};

判断一个树是不是二叉树->判断一个树的高度

height == -1 左右子树不是平衡二叉树，或者高度差大于1

height == 0 空树

height == 非0，真实的高度