力扣-剑指Offer 55-II题 平衡二叉树（C++）- dfs

题目链接：https://leetcode-cn.com/problems/ping-heng-er-cha-shu-lcof/
题目如下：

class Solution {
public:
    bool isBalanced(TreeNode* root) {
        dfs(root);
        return res;
    }
    int dfs(TreeNode* root){
        if(root==nullptr) return 0;
        if(res==false) return 0;//用于提前终止递归

        int left=dfs(root->left);
        int right=dfs(root->right);

        if(abs(left-right)>1) res=false;

        return max(left,right)+1;
    }
private:
    bool res=true;
};