题目:https://leetcode-cn.com/problems/binary-tree-preorder-traversal/
代码:
class Solution { public List<Integer> preorderTraversal(TreeNode root) { List<Integer> res = new ArrayList<>(); if (root != null) { res.add(root.val); res.addAll(this.preorderTraversal(root.left)); res.addAll(this.preorderTraversal(root.right)); } return res; } }
参考:94. 二叉树的中序遍历