难度:简单
https://leetcode.cn/problems/binary-tree-preorder-traversal/
给你二叉树的根节点 root ,返回它节点值的 前序 遍历。
输入:root = [1,null,2,3]
输出:[1,2,3]
输入:root = []
输出:[]
输入:root = [1]
输出:[1]
输入:root = [1,2]
输出:[1,2]
输入:root = [1,null,2]
输出:[1,2]
import type { TreeNode } from '~/utils/treeNode'
export function preorderTraversal(root: TreeNode | null): number[] {
const res: number[] = [];
const fn = (node: TreeNode | null) => {
if (!node) return
res.push(node.val);
fn(node.left);
fn(node.right);
}
fn(root);
return res;
}