590. N-ary Tree Postorder Traversal

Easy
Given the root of an n-ary tree, return the postorder 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:
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Input: root = [1,null,3,2,4,null,5,6]
Output:
[5,6,3,2,4,1]
Example 2:
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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:
[2,6,14,11,7,3,12,8,4,13,9,10,5,1]
Constraints:
  • The number of nodes in the tree is in the range [0, 104].
  • 0 <= Node.val <= 104
  • The height of the n-ary tree is less than or equal to 1000.
Follow up: Recursive solution is trivial, could you do it iteratively?

解題

145. 的姐妹題
Runtime: 0 ms, faster than 100%
Memory Usage: 4.1 MB, less than 27.94%
/**
* Definition for a Node.
* type Node struct {
* Val int
* Children []*Node
* }
*/
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func postorder(root *Node) []int {
res := make([]int, 0)
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var helper func(*Node)
helper = func(root *Node) {
if root == nil { return }
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for _, child := range root.Children {
helper(child)
}
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res = append(res, root.Val)
}
​
helper(root)
​
return res
}
​