leetcode之balanced-binary-tree(平衡二叉树判断)

题目

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.

题意

给定一个二叉树，判定它是不是一个平衡二叉树，什么是一个平衡二叉树，就是这个二叉树上的每一个节点下的子树，其左子树的长度和右子树的长度之差不超过1.

解题思路

这里直接递归遍历每一个节点，通过递归dfs获取其节点的左子树和右子树的长度，然后对其进行判断既可。

C++实现代码

/**
 * 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 == nullptr)
            return true;
        if(abs(dfs(root->left)-dfs(root->right))>1)
            return false;
        return isBalanced(root->left) && isBalanced(root->right);
    }
    int dfs(TreeNode* root){
        int depth =0;
        if(root == nullptr)
            return 0;
        return max(dfs(root->left),dfs(root->right))+1;
    }
    
};