描述
Given the root of an n-ary tree, return the preorder traversal of its nodes' values.
Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)
Example 1:
Input: root = [1,null,3,2,4,null,5,6]
Output: [1,3,5,6,2,4]
Example 2:
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]
Note:
The number of nodes in the tree is in the range [0, 10^4].
0 <= Node.val <= 10^4
The height of the n-ary tree is less than or equal to 1000.
解析
根据题意，就是对 N 叉树进行前序遍历，只需要进行递归，按照对每个二叉子树进行先根后左再右的顺序进行遍历即可，与二叉树不同的是，这里需要对所有的分叉进行遍历，而不只是左右两个子树。
解答
"""
# Definition for a Node.
class Node(object):
def __init__(self, val=None, children=None):
self.val = val
self.children = children
"""
class Solution(object):
def preorder(self, root):
"""
:type root: Node
:rtype: List[int]
"""
r = []
def pre(root):
if not root:
return
r.append(root.val)
for child in root.children:
pre(child)
pre(root)
return r
运行结果
Runtime: 48 ms, faster than 39.55% of Python online submissions for N-ary Tree Preorder Traversal.
Memory Usage: 16.4 MB, less than 76.08% of Python online submissions for N-ary Tree Preorder Traversal.
原题链接：leetcode.com/problems/n-…
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