Remove Nth Node From End of List

Given a linked list, remove the nth node from the end of list and return its head.

Notice

The minimum number of nodes in list is n.

Example

Given linked list: 1->2->3->4->5->null, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5->null.

Challenge

Can you do it without getting the length of the linked list?

分析：

为了删除倒数第n个node,我们需要找到那个node的parent，然后parent.next = parent.next.next. 这里我们创建一个dummy node用来处理删除的是第一个node的情况。

 public class Solution {
     public ListNode removeNthFromEnd(ListNode head, int n) {
         ListNode dummy = new ListNode();
         dummy.next = head;

         ListNode parent = dummy;
         for (int i = ; i < n; i++) {
             if (head == null) {
                 return null;
             }
             head = head.next;
         }
         while (head != null) {
             head = head.next;
             parent = parent.next;
         }
         parent.next = parent.next.next;
         return dummy.next;
     }
 }

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