力扣第104题-二叉树的最大深度

题目
再写个简单题爽爽
题目链接

题解

/**
 * 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) {
        return dfs(root);
    }

    /**
     * 方法返回当前节点之下（包含当前节点）一共有几层
     */
    private int dfs(TreeNode node) {
        // 当前节点也是空返回0
        if (node == null) {
            return 0;
        }
        // 左右子树都为空返回1
        if (node.left == null && node.right == null) {
            return 1;
        }
        // 左子树和右子树取个最大值再加上本层
        return Math.max(dfs(node.left), dfs(node.right)) + 1;
    }
}