104. Maximum Depth of Binary Tree

目录

• 题目描述
• 方法1
• 方法2

题目描述

Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the
longest path from the root node down to the farthest leaf node.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

方法1

递归解法

class Solution {
public:
    int maxDepth(TreeNode *root) {
        
        if(!root) return 0;
        if(!root->left) 
            return maxDepth(root->right)+1;
        if(!root->right) 
            return maxDepth(root->left)+1;
        return max(maxDepth(root->left),maxDepth(root->right))+1;
    }
};

方法2

树的层次遍历

class Solution {
public:
    int maxDepth(TreeNode *root) {

        if(root==nullptr) 
            return 0;
        queue<TreeNode*> q;
        q.push(root); 
        int depth=0;
        while(!q.empty())
        {   
            //我们将这一层有节点触发depth的更新
            //而我们对depth的更新放在了进入循环的开始部分
            //所以depth合理的初始化为了0
            depth++;
            int n = q.size();
            while(n--)  
            {
                TreeNode * currentNode =q.front();
                q.pop();
                if(currentNode->left!=nullptr)
                    q.push(currentNode->left);
                if(currentNode->right!=nullptr)
                    q.push(currentNode->right);        
            }
        }
        return depth;       
    }
};