/**
 * 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) {

        if (root == null) {
            return 0;
        }

        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;

    }

}

Create : 104 Maximum Depth of Binary Tree
Create : 104 Maximum Depth of Binary Tree
