[Leetcode] Balanced Binary Tree

Balanced Binary Tree Oct 9 '12 7722 / 18479

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 ofevery node never differ by more than 1.

看清题目很重要！

这里balance的定义：任意子树的depth，相差都不超过1。

其实，我觉得balance的定义还可以是另外一种：任意两个叶节点（这里叶节点为null节点）的depth相差不超过1。这样的话，方法就变一下。不过大体还是相同的。

/**
 * 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 isBalanced(TreeNode *root) {
        int l;
        return check(root, l);
    }
    
    bool check(TreeNode* cur, int &len) {
        if (cur == 0) {
            len = 0;
            return true;
        }
        
        int l, r;
        if (check(cur->left, l) && check(cur->right, r)) {
            len = max(l, r) + 1;
            return abs(l - r) <= 1;
        }
        return false;
    }
};