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);}
}