如何删除链表的第一个节点？

Question

我正在为我的数据结构 class 开发一个项目，该项目要求我编写一个 class 来实现一个整数链表。

Use an inner class for the Node.

Include the methods below.

Write a tester to enable you to test all of the methods with whatever data you want in any order.

我必须创建一个名为“public int deleteFromFront()”的方法。此方法旨在“删除列表前面的节点和 return 其中的 int，如果列表为空，则为 null。”我在下面有这个方法的代码。但是，当我测试此方法时，我得到了错误的输出。它应该 return 被删除的节点的值或者如果列表为空则为 null。因此，例如，如果我有一个像这样的列表“4 3 10 11 3 15 6 11 18 17”并且我想删除第一个节点，该方法应该 return 4 因为 4 是第一个节点。虽然该方法确实删除了 4 它 returns 3 新头的值。有人知道我做错了什么吗？以及如何解决？

import java.util.Random;
import java.util.Scanner;

public class LinkedListOfInts {
    Node head;
    Node tail;

    private class Node {
        int value;
        Node nextNode;

        public Node(int value, Node nextNode) {
            this.value = value;
            this.nextNode = nextNode;
        }

    }

    public LinkedListOfInts(LinkedListOfInts other) {
        Node tail = null;
        for (Node n = other.head; n != null; n = n.nextNode) {
            if (tail == null)
                this.head = tail = new Node(n.value, null);
            else {
                tail.nextNode = new Node(n.value, null);
                tail = tail.nextNode;
            }
        }
    }

    public LinkedListOfInts(int[] other) {
        Node[] nodes = new Node[other.length];
        for (int index = 0; index < other.length; index++) {
            nodes[index] = new Node(other[index], null);
            if (index > 0) {
                nodes[index - 1].nextNode = nodes[index];
            }
        }

        head = nodes[0];
    }

    public LinkedListOfInts(int N, int low, int high) {
        Random random = new Random();
        for (int i = 0; i < N; i++)
            this.addToFront(random.nextInt(high - low) + low);
    }

    public void addToFront(int x) {
        head = new Node(x, head);
    }

    public int deleteFromFront() {
        if (head == null)
            return -1;
        else {
            if (head == tail) {
                head = null;
                tail = null;
            } else {
                head = head.nextNode;
            }
        }
        return head.value;
    }

    public String toString() {
        String result = " ";
        for (Node ptr = head; ptr != null; ptr = ptr.nextNode)
            result += ptr.value + " ";
        return result;
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        LinkedListOfInts list = new LinkedListOfInts(10, 1, 20);
        LinkedListOfInts copy = new LinkedListOfInts(list);
        boolean done = false;
        while (!done) {
            System.out.println("1. Delete from Front");
            System.out.println("2. toString");
            switch (input.nextInt()) {
            case 1:
                System.out.println("Delete an Item at the Front of the List");
                System.out.println(list.deleteFromFront());
                break;
            case 2:
                System.out.println("toString");
                System.out.println(list.toString());
                break;
            }
        }
    }
}

Answer 1

您应该将旧的 head 节点值保存在一个变量中，稍后删除 head node。稍后，您应该 return 这个变量。

  public int deleteFromFront() {
        int headValue = -1;
        if (head == null)
            return headValue;
        else {
            if (head == tail) {
                head = null;
                tail = null;
            } else {
                headValue = head.value;
                head = head.nextNode;
            }
        }
        return headValue;
    }

如何删除链表的第一个节点？

How do I delete the first node of a Linked List?

java

linked-list

nodes

data-structures