【LeetCode OJ】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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    private int max = 0;
    public void preOrder(TreeNode root, int depth){
		if(root == null)return;
		preOrder(root.left, depth + 1);
		if(max < depth) max = depth;
		preOrder(root.right, depth + 1);
	}
    public int maxDepth(TreeNode root) {
		preOrder(root, 1);
		return max;        
    }
}