leetcode -- 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.

Recursive Version

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(root == null){
            return 0;
        }
        int left = 0, right = 0;
        if(root.left != null){
            left = maxDepth(root.left);
        }
        
        if(root.right != null){
            right = maxDepth(root.right);    
        }
        
        return 1 + Math.max(left, right);
    }
}