LeetCode 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; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) return 0;
        int leftD = 1, rightD = 1;
        int leftDepth = getDepth(root.left, leftD);
        int rightDepth = getDepth(root.right, rightD);
        return (leftDepth > rightDepth) ? leftDepth : rightDepth;
    }
    
    public static int getDepth(TreeNode root, int d) {
        int leftDepth, rightDepth;
        if (root == null) return d;
        else d++;
        leftDepth = getDepth(root.left, d);
        rightDepth = getDepth(root.right, d);
        return (leftDepth > rightDepth) ? leftDepth : rightDepth;
    }
}