104. Maximum Depth of Binary Tree

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