java - 编写一个方法 cut(LinkList x)，将列表 x 分成两个(大致)相等的两半，并将后半部分放在前半部分的前面

Question

示例:在链表上调用 cut 方法:

f{1, 2, 3, 4, 5, 6, 7}

将返回链接列表:

f{5,6, 7, 1, 2, 3, 4}

LinkList Cut() 方法

public static LinkList Cut(LinkList x) {
        LinkList front = new LinkList();
        LinkList back = new LinkList();
        while(!x.isEmpty){
            front.insertLast(x.removeFirst().data);
            if(!x.isEmpty){
                back.insertFirst(x.removeLast().data);
            }
        }
        while(!back.isEmpty){
            front.insertFirst(back.removeLast().data);

        }
        return front;

       }

第一个和最后一个、删除和插入方法。

public void insertFirst(int data){
        start = new Node(0);
        if(start == null){
            System.out.println("list is empty if");
        }else{
            start.link = head.link;
            start.data = 20;
            head.link = start;
        }
    }

    public void insertLast(int data) {

        start = new Node(0);
        if(start == null){
            System.out.println("List is empty il");
        }else{
            ptr = head;
            while(ptr.link != null){
                ptr = ptr.link;
            }
            ptr.link = start;
            start.data = 20;
        }
    }

    public Node removeFirst(){
        ptr = head.link;
        if(ptr == null){
            System.out.println("The list is empty");
        }else{
            ptr1 = ptr.link;
            head.link = ptr1;
        }
        return ptr;
    }

    public Node removeLast() {
        ptr = head;
        if(ptr.link == null)
        {
            System.out.println("List is Empty rl");
        }else{
            while(ptr.link != null){
                ptr1 = ptr;
                ptr = ptr.link;
            }
            ptr1.link = null;
        }
        return ptr;
    }

main();

LinkList list = new LinkList();
LinkList.head = new Node(1);
LinkList.head.link = new Node(2);
LinkList.head.link.link = new Node(3);
LinkList.head.link.link.link = new Node(4);
LinkList.head.link.link.link.link = new Node(5);
LinkList.head.link.link.link.link.link = new Node(6);
LinkList.head.link.link.link.link.link.link = new Node(7);
System.out.println("Link List Element: ");
list.printList(head);
list.Cut(list);
System.out.println("");
System.out.println("Cut Half Link List Element: ");
list.printList(head);

输出。

Link List Element: 
1 
2 
3 
4 
5 
6 
7 
The list is empty

我的代码有什么问题，为什么显示列表为空

Answer 1

这可以通过将列表的“头”链接到其“尾部”并更新头的简单而直接的方法来实现。

下面的函数返回更新后的列表头。(C++)。

Node *CutTheList(Node *head)
{
  int sizeList=0;  // Contains the size of the List
  Node *tracker=head; // temporary tracker

  while(tracker!=NULL){ sizeList++; tracker=tracker->next;} // Counts the Size of the List
  tracker=head;

  while(tracker->next!=NULL){tracker=tracker->next;} // Assigns the head to tail.
  tracker->next=head;

  int sizehalf=sizeList/2; //Size of the halved List.
  tracker=head;

  while(--sizehalf){ tracker=tracker->next; } //Update the head
  head=tracker->next; 
  tracker->next=NULL;

  return head;
 }