(Leet Code c++)Maximum Depth of Binary Tree

 

104. Maximum Depth of Binary Tree

Easy

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Given the root of a binary tree, return its maximum depth.

A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

 

Example 1:

Input: root = [3,9,20,null,null,15,7] Output: 3

Example 2:

Input: root = [1,null,2] Output: 2

Example 3:

Input: root = [] Output: 0

Example 4:

Input: root = [0] Output: 1

 

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• -100 <= Node.val <= 100

 

이진 트리의 depth를 구하면 된다.

root가 널이 아닌 경우 dfs() 함수를 통해 depth를 구한다.

left와 right의 depth를 구하여, 현재 depth와 left, right의 depth 중 가장 큰 값을 리턴하면 된다.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int dfs(TreeNode * node, int current){
        int left = 0;
        int right = 0;
        
        if(node->left != NULL){
            left = dfs(node->left, current + 1);
        }
        
        if(node->right != NULL){
            right = dfs(node->right, current + 1);
        }
        
        current = max(current, max(left, right));
        
        return current;
    }
    
    int maxDepth(TreeNode* root) {
        int answer = 0;
        
        if(root != NULL){
            answer = dfs(root, 1);
        }
        
        return answer;
    }
};