方法一：双指针

思路：采用保持距离的双指针

  1. /**
  2.  * Definition for singly-linked list.
  3.  * type ListNode struct {
  4.  *     Val int
  5.  *     Next *ListNode
  6.  * }
  7.  */
  8. func removeNthFromEnd(head *ListNode, n int) *ListNode {
  9.     dummyNode := &ListNode{}
  10.     dummyNode.Next = head
  12.     //删除倒数第n个节点我们需要保持n+1的距离
  13.     fast, slow := dummyNode, dummyNode
  14.     for i := 0; i < n+1; i++ {
  15.         //如果n越界，直接返回空
  16.         if fast == nil {
  17.             return dummyNode.Next
  18.         }
  19.         fast = fast.Next
  20.     }
  22.     for fast != nil {
  23.         fast, slow = fast.Next, slow.Next
  24.     }
  26.     //此时slow指向倒数第n个节点的前1个节点
  27.     slow.Next = slow.Next.Next
  28.     return dummyNode.Next
  29. }