【剑指OFFER】平衡二叉树

题目描述
输入一棵二叉树，判断该二叉树是否是平衡二叉树。
方法1：

class Solution {
public:
    bool IsBalanced_Solution(TreeNode* pRoot) {
        if(!pRoot) return true;
        return abs(maxDeepth(pRoot->left)-maxDeepth(pRoot->right))<=1 && IsBalanced_Solution(pRoot->left) && IsBalanced_Solution(pRoot->right);
    }
    int maxDeepth(TreeNode* pRoot){
        if(!pRoot)return 0;
        return 1+max(maxDeepth(pRoot->left),maxDeepth(pRoot->right));
    }
};

方法2：剪接，防止求深度的时候，重复遍历。

class Solution {
public:
    bool IsBalanced_Solution(TreeNode* pRoot) {
        return maxDeepth(pRoot)!=-1;
    }
    int maxDeepth(TreeNode* pRoot){
        if(!pRoot)return 0;
        int left = maxDeepth(pRoot->left);
        if(left==-1)return -1;
        int right = maxDeepth(pRoot->right);
        if(right==-1)return -1;
        return abs(left-right)<=1?max(left,right)+1:-1;
    }
};