Leetcode 590

The First Solution:

This solution seems pretty self-explanatory.

func postorder(root *Node) []int {
    return helper(root, []int{})
}

func helper(r *Node, l []int)[]int{
    if r != nil{
        for _,item := range r.Children{
            l = helper(item,l)
        }
        l = append(l,r.Val)        
    }
    return l
}

The Second Solution:

If you look at the following code and don’t understand, it is probably because of: r.Children[len(r.Children) - i - 1], but if you look at it carefully, you will see that it is the same as reversing r.Children except cleaner.

func postorder(root *Node) []int {
    return helper(root, []int{})
}

func helper(r *Node, l []int) []int {
    if r != nil {
        l = append(l[:0], append([]int{r.Val}, l[0:]...)...)
        for i := range r.Children {
            l = helper(r.Children[len(r.Children) - i - 1], l)
        }
    }
    return l
}