题解 | 【模板】链表

import java.util.List;
import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        MyLinkedList list = new MyLinkedList();
        int count = 0;
        if (in.hasNextLine())
            count = Integer.parseInt(in.nextLine());
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine() && (count--) > 0) {
            String[] arr = in.nextLine().split(" ");
            String ListOperation = arr[0];
            if (ListOperation.equals("insert")) {
                list.insertNode(Integer.parseInt(arr[1]), Integer.parseInt(arr[2]));
            } else if (ListOperation.equals("delete")) {
                list.deleteNode(Integer.parseInt(arr[1]));
            } else {
                System.out.println("非法输入");
            }
        }
        System.out.println(list);
    }
}

class MyLinkedList {
    ListNode head;

    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        if (head == null)
            return "NULL";
        else {
            ListNode node = head;
            while (node != null) {
                stringBuilder.append(node.val + " ");
                node = node.next;
            }
        }
        return stringBuilder.toString();
    }

    public void insertNode(int x, int y) {
        // 首次插入(长度为0时）
        if (head == null) {
            head = new ListNode(y);
            return;
        }
        // 后续插入
        ListNode l = head, ll = l;

        // 长度为1时或head刚好匹配上
        if (head.val == x) {
            ll = head;
            head = new ListNode(y);
            head.next = ll;
            return;
        }

        // 长度>=2时且不考虑head刚好匹配上的情况
        while (l.next != null) {
            ll = l;
            l = l.next;
            if (l.val == x) {
                ll.next = new ListNode(y);
                ll.next.next = l;
                return;
            }
        }

        l.next = new ListNode(y);//末尾插入
    }

    public void deleteNode(int val) {
        // write code here
        ListNode l = head, mid;
        if (head == null)
            return;
        if (head.val == val)
            head = head.next;

        for (mid = l.next; mid != null; ) {

            if (mid.val == val) {
                l.next = mid.next;
                mid.next = null;
                break;
            } else {
                l = l.next;
                mid = mid.next;
            }
        }
    }
}

class ListNode {
    int val;
    ListNode next;

    public ListNode(int val) {
        this.val = val;
    }

}

这题是真的坑啊，很多细节和情况需要考虑。