leetcode 平衡二叉树判断

问题描述：

https://oj.leetcode.com/problems/balanced-binary-tree/点击打开链接

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.

示例代码：

/**
 * 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) 
    {
        if (!root) return true;
        int lh = height(root->left);
        int rh = height(root->right);
        int diff = lh > rh ? lh - rh : rh - lh;
        if (diff > 1) return false;
        return isBalanced(root->left) && isBalanced(root->right);
    }
    int height(TreeNode *root)   
    {  
        if (!root) return 0;  
        int lh = height(root->left);  
        int rh = height(root->right);  
        return lh > rh ? lh + 1 : rh + 1;  
    }  
};

该题有可以优化的地方：做了不必要的递归，计算高度和左右子树的判定能否合并？？