• 原题连接：19. 删除链表的倒数第 N 个结点

1- 思路

双指针

• 定义 dummyHead 处理头结点情况
• slow 指针：初始化为 dummyHead 定位到被移除元素的前一个
• fast 指针：初始化诶 dummyHead ，从 dummyHead 开始 先移动 n 位
• 之后 同时移动 slow 和 fast ，终止条件是 while(fast.next!=null)

2- 实现

⭐19. 删除链表的倒数第 N 个结点——题解思路

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        // 双指针
        // 定义 dummy
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;

        ListNode slow = dummyHead;
        ListNode fast = dummyHead;
        for(int i = 0 ; i < n;i++){
            fast = fast.next;
        }
        while(fast.next!=null){
            slow = slow.next;
            fast = fast.next;
        }
        // slow 定位到前
        slow.next = slow.next.next;
        return dummyHead.next;
    }
}

3- ACM 实现

public class removeN {
    public static class ListNode {
        int val;
        ListNode next;
        ListNode(int x) {
            val = x;
            next = null;
        }
    }

    public static ListNode removeNthFromEnd(ListNode head, int n) {
        // 双指针
        // 定义 dummy
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;

        ListNode slow = dummyHead;
        ListNode fast = dummyHead;
        for(int i = 0 ; i < n;i++){
            fast = fast.next;
        }
        while(fast.next!=null){
            slow = slow.next;
            fast = fast.next;
        }
        // slow 定位到前
        slow.next = slow.next.next;
        return dummyHead.next;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
// 读取第一个链表的节点数量
        int n1 = sc.nextInt();
        ListNode head1 = null, tail1 = null;
        for (int i = 0; i < n1; i++) {
            int val = sc.nextInt();
            ListNode newNode = new ListNode(val);
            if (head1 == null) {
                head1 = newNode;
                tail1 = newNode;
            } else {
                tail1.next = newNode;
                tail1 = newNode;
            }
        }
        System.out.println("输入n");
        int nth = sc.nextInt();
        ListNode forRes = removeNthFromEnd(head1,nth);
        while(forRes!=null){
            System.out.print(forRes.val+"");
            forRes = forRes.next;
        }
    }
}