Leetcode Everyday: 104. Maximum Depth of Binary Tree

https://leetcode.com/problems/maximum-depth-of-binary-tree/

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 a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        return dfs(root);
    }
    
    public int dfs(TreeNode root){
        if(root == null) return 0;
        int left = 1+dfs(root.left);
        int right = 1+dfs(root.right);
        return Math.max(left,right);
    }
    
}

Handle the null case in the dfs.