学步园

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.

判断给定的树是否是平衡的，比较简单，两个条件：左右子树都是平衡的；左右高度差值小于等于1；

判断左右子树的过程我们可以放在求高度中，把原始的求高度的递归算法改一下就好了。

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int h=0;
        return check(root,h);
    }
    bool check(TreeNode* root,int& h)
    {
        if ( !root )
        {
            h=0;
            return true;
        }
        int lh=0,rh=0;
        bool ans=check(root->left,lh)&&check(root->right,rh);
        if (ans)
        {
            h=max(lh,rh)+1;
        }
        return ans&&(lh-rh<=1&&lh-rh>=-1);
    }
};