Leetcode 589. N-ary Tree Preorder Traversal

DFS,两种实现方式,递归和栈.

"""
# Definition for a Node.
class Node:
    def __init__(self, val, children):
        self.val = val
        self.children = children
"""
class Solution:
    def preorder(self, root: 'Node') -> List[int]:
        if not root:
            return []
        stack,ans=[root],[]
        while stack:
            node=stack.pop()
            ans.append(node.val)
            if node.children:
                stack.extend(reversed(node.children))
        return ans

"""
# Definition for a Node.
class Node:
    def __init__(self, val, children):
        self.val = val
        self.children = children
"""
class Solution:
    def preorder(self, root: 'Node') -> List[int]:
        if not root:
            return []
        ans=[root.val]
        for c in root.children:
            ans+=self.preorder(c)
        return ans