【2022初春】【LeetCode】104. 二叉树的最大深度

还是差了点细节，增加层数不用在res里增加

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

    }
}