19. Remove Nth Node From End of List java solutions

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

For example,

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

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

Note:
Given n will always be valid.
Try to do this in one pass.

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if(head == null || head.next == null) return null;
        ListNode slow = head;
        ListNode fast = head;
        while(n>1){
            fast = fast.next;
            n--;
        }
        ListNode pre = new ListNode(-1);
        pre.next = slow;
        while(fast.next != null){
            pre = pre.next;
            slow = slow.next;
            fast = fast.next;
        }
        pre.next = pre.next.next;
        if(slow == head) return pre.next;//如果删除的倒N个节点是头结点的话，做一下特殊处理
        else return head;
    }
}