19. 删除链表的倒数第 N 个结点

19. 删除链表的倒数第 N 个结点

原题

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode slow = head;
        ListNode fast = head;
        //使得fast和slow之间相隔n-1个节点(fast比slow先走n步)
        for(int i=0;i<n;i++){
            fast=fast.next;
        }
        //说明删除的是头结点
        if(fast==null){
            return head.next;
        }
        //依次向后移动
        while(fast.next!=null){
            slow=slow.next;
            fast=fast.next;
        }
        //将slow指向下一个节点的后继结点（不能写slow.next=fast,举例[1,2]）
        slow.next=slow.next.next;
        //返回结果
        return head;
    }
}
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