使用第三个引用对两个链表进行递归合并排序

Question

我正在尝试使用第三个引用来解决递归合并排序。我想获取第三个参考，并继续按排序顺序链接两个链表（两个链表单独排序）中的节点，而不创建任何额外的节点。

我看到有一个递归程序引用了here。但是我想使用第三个参考来尝试这个，但我一直把它搞砸了。谁能让我知道我在这里缺少什么条件？

import java.util.ArrayList;
import java.util.ListIterator;

public class MergeLinkedListsIntoExisting {
    public static void main(String[] args){
        Node nodeList1 = null, nodeList2 = null;
        Node temp = null;
        ArrayList<Integer> array1 = new ArrayList<Integer>();
        array1.add(3);
        array1.add(7);
        array1.add(9);

        ArrayList<Integer> array2 = new ArrayList<Integer>();
        array2.add(1);
        array2.add(2);
        array2.add(8);

        nodeList1 = add(nodeList1, array1);
        nodeList2 = add(nodeList2, array2);
        System.out.println("**List 1**");
        print(nodeList1);
        System.out.println("**List 2**");
        print(nodeList2);
        System.out.println("Sorted List");
        Node nodeList3 = mergeTwoLists(nodeList1, nodeList2, temp);
        print(nodeList3);
    }
    private static Node add(Node node, ArrayList<Integer> list){
        Node current = node;
        Node head = node;
        ListIterator<Integer> it = list.listIterator();
        while(it.hasNext()){
            if(head==null){
                head = new Node();
                head.data = it.next();
                head.next=null;
                node = head;
            }
            else{
                current = new Node();
                current.data = it.next();
                current.next = null;
                node.next = current;
                node = node.next;
            }
        }
        return head;
    }

    private static void print(Node node) {
        if(node!=null){
            while(node.next!=null){
                System.out.print(node.data + " ");
                node = node.next;
            }
            System.out.println(node.data);
        }
        else{
            System.out.println("No elements in the linkedList.");
        }
    }


    private static Node mergeTwoLists(Node nodeList1, Node nodeList2, Node temp) {
        if(nodeList1 == null) return nodeList2;
        if(nodeList2 == null) return nodeList1;

        if(nodeList1.data <= nodeList2.data){
            if(temp == null){
                temp = nodeList1;
                temp.next = mergeTwoLists(nodeList1.next, nodeList2, temp.next);
            }
            else{
                System.out.println(temp.data);
                temp.next = mergeTwoLists(nodeList1.next, nodeList2, temp.next);
            }
        }else{
            if(temp == null){
                temp = nodeList2;
                System.out.println(temp.data);
                temp.next = mergeTwoLists(nodeList1, nodeList2.next, temp.next);
            }
            else{
                System.out.println(temp.data);
                temp.next = mergeTwoLists(nodeList1, nodeList2.next, temp.next);
            }
        }
        return temp;
    }
}

解析应该在mergeTwoLists的递归调用中使用temp.next。根据需要纠正我和我的方法。

Answer 1

如果你想要递归方法

private static Node mergeTwoLists(Node nodeList1, Node nodeList2) {
    if(nodeList1 == null) return nodeList2;
    if(nodeList2 == null) return nodeList1;
    Node tmp = new Node();
    if(nodeList1.data <= nodeList2.data){
        tmp.data = nodeList1.data;
        tmp.next = mergeTwoLists(nodeList1.next, nodeList2);
    }else{
        tmp.data = nodeList2.data;
        tmp.next = mergeTwoLists(nodeList1, nodeList2.next);
    }
    return temp;
}

Answer 2

编辑：我刚刚又看了一遍，我认为修复代码的主要修改只是删除了 temp 等于 null 的特殊情况。

我刚刚修改了您的代码并使其正常工作。只需通过temp 而不是temp.next，如果 temp 为 null，则不需要特殊情况。

import java.util.ArrayList;
import java.util.ListIterator;

public class MergeLinkedListsIntoExisting {
    public static void main(String[] args){
        Node nodeList1 = null, nodeList2 = null;
        Node temp = null;
        ArrayList<Integer> array1 = new ArrayList<Integer>();
        array1.add(3);
        array1.add(7);
        array1.add(9);

        ArrayList<Integer> array2 = new ArrayList<Integer>();
        array2.add(1);
        array2.add(2);
        array2.add(8);

        nodeList1 = add(nodeList1, array1);
        nodeList2 = add(nodeList2, array2);
        System.out.println("**List 1**");
        print(nodeList1);
        System.out.println("**List 2**");
        print(nodeList2);
        System.out.println("Sorted List");
        Node nodeList3 = mergeTwoLists(nodeList1, nodeList2, temp);
        print(nodeList3);
    }
    private static Node add(Node node, ArrayList<Integer> list){
        Node current = node;
        Node head = node;
        ListIterator<Integer> it = list.listIterator();
        while(it.hasNext()){
            if(head==null){
                head = new Node();
                head.data = it.next();
                head.next=null;
                node = head;
            }
            else{
                current = new Node();
                current.data = it.next();
                current.next = null;
                node.next = current;
                node = node.next;
            }
        }
        return head;
    }

    private static void print(Node node) {
        if(node!=null){
            while(node.next!=null){
                System.out.print(node.data + " ");
                node = node.next;
            }
            System.out.println(node.data);
        }
        else{
            System.out.println("No elements in the linkedList.");
        }
    }


    private static Node mergeTwoLists(Node nodeList1, Node nodeList2, Node temp) {
        if(nodeList1 == null) return nodeList2;
        if(nodeList2 == null) return nodeList1;

        if(nodeList1.data <= nodeList2.data){

          temp = nodeList1;
          temp.next = mergeTwoLists(nodeList1.next, nodeList2, temp);

        }else{

          temp = nodeList2;
          temp.next = mergeTwoLists(nodeList1, nodeList2.next, temp);                
        }
        return temp;
    }
}

public class Node{
    int data;
    Node next;
}