Leetcode 144. 二叉树的前序遍历

题目描述

题目链接：https://leetcode.cn/problems/binary-tree-preorder-traversal/description/

代码实现

class Solution {
    List<Integer> l  = new ArrayList<>();
    public List<Integer> preorderTraversal(TreeNode root) {
        preoder(root);
        return l;
    }
    public void preoder(TreeNode root){
        if(root==null){
            return;
        }
        l.add(root.val);
        preoder(root.left);
        preoder(root.right);
    }
}