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:

Input: root = [1,null,3,2,4,null,5,6]
Output:
 [5,6,3,2,4,1]

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:
 [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
 * }
 */

func postorder(root *Node) []int {
    res := make([]int, 0)

    var helper func(*Node) 
    helper = func(root *Node) {
        if root == nil { return }

        for _, child := range root.Children {
            helper(child)
        }

        res = append(res, root.Val)
    }

    helper(root)

    return res
}