leetcode Balanced Binary Tree 后序遍历思想避免重复遍历结点

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.

用一个变量保存当前结点的深度

/**
 * 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 depth = 0;
        return isBalance(root,&depth);
    }
    bool isBalance(TreeNode* root, int* depth) {
        if(root == NULL) {
            *depth = 0;
            return true;
        }
        int left,right;
        if(isBalance(root->left,&left) && isBalance(root->right,&right)) {
            int dif = left-right;
            if(dif<=1 && dif>=-1) {
                *depth = left>right?left+1:right+1;
                return true;
            }
        }
        return false;
    }
};