题解 | #【模板】链表#

import java.util.Scanner;

class MyLinkedList {
    static class ListNode {
        public int val;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    };
    //带头链表
    private ListNode head;
    //打印链表
    public void display() {
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        if (head == null) {
            System.out.println("NULL");
        }
    }

    //尾插
    public void addLast(int val) {
        ListNode node = new ListNode(val);
        if (head == null) {
            head = node;
            return;
        }
        ListNode cur = head;
        while (cur.next != null) {
            cur = cur.next;
        }
        cur.next = node;
    }
    //在指定x位置插入
    public void insert(int key, int val) {
        ListNode node = new ListNode(val);
        ListNode dummy = new ListNode(-1);
        ListNode pre = dummy;
        pre.next = head;
        ListNode next = pre.next;
        while (next != null ) {
            if (next.val == key) {
                node.next = next;
                pre.next = node;
                head = dummy.next;
                return;
            }
            pre = pre.next;
            next = next.next;
        }
        addLast(val);
        
    }

    //删除第一次出现的key值
    public void delete(int key) {
        if (head != null && head.val == key) {
            head = head.next;
            return;
        }
        ListNode dummyHead = new ListNode(0);
        dummyHead.next = head;
        ListNode pre = dummyHead;
        ListNode cur = pre.next;
        while (cur != null) {
            if (cur.val == key) {
                pre.next = cur.next;
                return;
            }
            pre = pre.next;
            cur = cur.next;
        }    
    }



}
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = Integer.parseInt(in.nextLine());
        MyLinkedList list = new MyLinkedList();
        for (int i = 0; i < n; i++) {
            String[] data = in.nextLine().split(" ");
            switch(data[0]) {
                case "insert":
                    list.insert(Integer.parseInt(data[1]),Integer.parseInt(data[2]));
                    break;
                case "delete":
                    list.delete(Integer.parseInt(data[1]));
                    break;
            }
        }
        list.display();
        in.close();

    }
}