LeetCode 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 everynode never differ by more than 1.

 

这道题目总是理解错，最开始理解就是左子树的任何一个叶子节点和右子树的任何一个叶子节点的depth差不能大于1. 并且左右子树都是平衡的，所以设了leftMinDep, leftMaxDep,rightMinDep, rightMaxDep，然后minDep = min(leftMinDep, rightMinDep), maxDep = max(leftMaxDep, rightMaxDep), maxDep - minDep <= 1。

但看到红字，可以看到depth of a tree是定义为一棵树的节点最大深度，所以应该判断abs(leftTreeDep - rightTreeDep) <= 1。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool checkBalance(TreeNode *node, int &dep)
    {
        if (node == NULL)
        {
            dep = 0;
            return true;
        }
        
        int leftDep, rightDep;
        bool leftBalance = checkBalance(node->left, leftDep);
        bool rightBalance = checkBalance(node->right, rightDep);
        
        dep = max(leftDep, rightDep);
        
        return leftBalance && rightBalance && (abs(rightDep - leftDep) <= 1);
    }
    
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int dep;
        return checkBalance(root, dep);
    }
};