19. Remove Nth Node From End of List

Remove_Nth_Node_From_End_of_List.go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func removeNthFromEnd(head *ListNode, n int) *ListNode {
    count_from_last := 0
    return removeHelper(head, n, &count_from_last)
}

func removeHelper(node *ListNode, n int, count_from_last *int) *ListNode {
    
    if node == nil {
        return nil
    }
    node_next := removeHelper(node.Next, n, count_from_last)
  
    //走到最底後會開始往回走，所以可以接著做其他事

    node.Next = node_next // 更新 next(只有被刪除節點會回傳不同於原本的 next)
    
    *count_from_last++
    
    if *count_from_last == n {
        return node_next
    } 
    
    return node
}