小黑啃leetcode:589. N 叉树的前序遍历

递归法

class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children

class Solution:
    def preorder(self, root: 'Node') -> List[int]:
        # 定义存储数组
        arr = []
        def dfs(node):

            if node:
                arr.append(node.val)
                # 依次递归遍历孩子结点
                for child in node.children:
                    dfs(child)
        dfs(root)
        return arr

    

非递归法

class Solution:
    def preorder(self, root: 'Node') -> List[int]:
        if not root:
            return []
        stack = [root]
        display = []

        while stack:
            node = stack.pop()
            display.append(node.val)

            stack.extend(node.children[::-1])

        return display