Maximum Depth of Binary Tree

/**
 * 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) {
        if (root == null)
            return 0;
        int left = maxDepth(root.left);
        int right = maxDepth(root.right);
        int x = left>right ? left+1:right+1;
        return x;
    }
}