题目

• 原题连接：19. 删除链表的倒数第 N 个结点

1- 思路

模式识别：删除倒数第 n 个结点 ——> 定义 dummyHead 并用双指针实现删除逻辑

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) {
        if(head==null){
            return head;
        }
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        ListNode fast = dummyHead;
        ListNode slow = dummyHead;
        for(int i = 0 ; i < n ; i++){
            fast = fast.next;
        }

        while(fast.next!=null){
            slow = slow.next;
            fast = fast.next;
        }

        slow.next = slow.next.next;
        return dummyHead.next;
    }
}

3- ACM实现

public class removeLastN {

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

    public static ListNode removeLast(ListNode head,int n ){
        // 双指针
        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.next = slow.next.next;
        return dummyHead.next;
    }

    public static void main(String[] args) {
        Scanner sc  = new Scanner(System.in);
        System.out.println("输入链表长度");
        int n = sc.nextInt();
        System.out.println("输入链表元素");
        ListNode head = null,tail = null;
        for(int i = 0 ; i < n;i++){
            ListNode newNode = new ListNode(sc.nextInt());
            if(head==null){
                head = newNode;
                tail = newNode;
            }else{
                tail.next = newNode;
                tail = newNode;
            }
        }
        System.out.println("输入删除倒数第几个元素");
        int k = sc.nextInt();
        ListNode Res = removeLast(head,k);
        while(Res!=null){
            System.out.print(Res.val+" ");
            Res = Res.next;
        }
    }
}