JavaScript implements linked list insertion sort and linked list merge sort

This article introduces in detail the JavaScript implementation of linked list insertion sort and linked list merge sort. Linked list merge sort is to merge and sort each part and then merge them together.

1. Linked list

1.1 Storage representation of linked list

//链表的存储表示
typedef int ElemType;
typedef struct LNode
{
  ElemType data;
  struct LNode *next;
}LNode, *LinkList;

1.2 Basic operation

Create linked list:

/*
 * 创建链表。
 * 形参num为链表的长度，函数返回链表的头指针。
 */
LinkList CreatLink(int num)
{
  int i, data;
  
  //p指向当前链表中最后一个结点，q指向准备插入的结点。
  LinkList head = NULL, p = NULL, q;
  
  for (i = 0; i < num; i++)
  {
    scanf("%d", &data);
    q = (LinkList)malloc(sizeof(LNode));
    q->data = data;
    q->next = NULL;
    if (i == 0)
    {
      head = q;
    }
    else
    {
      p->next = q;
    }
    p = q;
  }
  return head;
}

Output linked list:

/*
 * 输出链表结点值。
 */
int PrintLink(LinkList head)
{
  LinkList p;
  for (p = head; p ;p = p->next)
  {
    printf("%-3d ", p->data);
  }
  return 0;
}

2. Linked list insertion sort

Basic idea: Assume that the first n-1 nodes are in order, insert the nth node Go to the appropriate position of the previous node and order these n nodes.

Implementation method:

Remove the first node on the linked list to become a linked list containing one node (head1), and the remaining nodes will naturally become another A linked list (head2), at this time head1 is an ordered linked list containing

one node;

Remove the first node from the linked list head2 and insert it into the linked list head1 At the appropriate position, head1 is still in order. At this time, head1 becomes an ordered linked list containing two nodes;

removes one node from the linked list head2 in turn and inserts it into the linked list head1. Until the linked list head2 is an empty linked list. Finally, the linked list head1 contains all nodes, and the nodes are in order.

Insertion sort code:

/*
 * 链表插入排序(由小到大)。
 * 输入：链表的头指针，
 * 输出：排序后链表的头指针。
 * 实现方法：将原链表拆成两部分：链表1仍以head为头指针，链表结点有序。链表2以head2为头指针，链表结点无序。
 * 将链表2中的结点依次插入到链表1中，并保持链表1有序。
 * 最后链表1中包含所有结点，且有序。
 */
LinkList LinkInsertSort(LinkList head)
{
  //current指向当前待插入的结点。
  LinkList head2, current, p, q;
  
  if (head == NULL)
    return head;
  
  //第一次拆分。
  head2 = head->next;
  head->next = NULL;
  
  while (head2)
  {
    current = head2;
    head2 = head2->next;
  
    //寻找插入位置，插入位置为结点p和q中间。
    for (p = NULL, q = head; q && q->data <= current->data; p = q, q = q->next);
  
    if (q == head)
    {
      //将current插入最前面。
      head = current;
    }
    else
    {
      p->next = current;
    }
    current->next = q;
  }
  return head;
}

Complete source code:

/*
 * 链表插入排序，由小到大
 */
#define _CRT_SECURE_NO_WARNINGS
#include 
#include 
 
#define TOTAL 10    //链表长度
 
//链表的存储表示
typedef int ElemType;
typedef struct LNode
{
  ElemType data;
  struct LNode *next;
}LNode, *LinkList;
 
LinkList CreatLink(int num);
LinkList LinkInsertSort(LinkList head);
int PrintLink(LinkList head);
 
/*
 * 创建链表。
 * 形参num为链表的长度，函数返回链表的头指针。
 */
LinkList CreatLink(int num)
{
  int i, data;
 
  //p指向当前链表中最后一个结点，q指向准备插入的结点。
  LinkList head = NULL, p = NULL, q;
 
  for (i = 0; i < num; i++)
  {
    scanf("%d", &data);
    q = (LinkList)malloc(sizeof(LNode));
    q->data = data;
    q->next = NULL;
    if (i == 0)
    {
      head = q;
    }
    else
    {
      p->next = q;
    }
    p = q;
  }
  return head;
}
 
/*
 * 链表插入排序(由小到大)。
 * 输入：链表的头指针，
 * 输出：排序后链表的头指针。
 * 实现方法：将原链表拆成两部分：链表1仍以head为头指针，链表结点有序。链表2以head2为头指针，链表结点无序。
 * 将链表2中的结点依次插入到链表1中，并保持链表1有序。
 * 最后链表1中包含所有结点，且有序。
 */
LinkList LinkInsertSort(LinkList head)
{
  //current指向当前待插入的结点。
  LinkList head2, current, p, q;
 
  if (head == NULL)
    return head;
 
  //第一次拆分。
  head2 = head->next;
  head->next = NULL;
 
  while (head2)
  {
    current = head2;
    head2 = head2->next;
 
    //寻找插入位置，插入位置为结点p和q中间。
    for (p = NULL, q = head; q && q->data <= current->data; p = q, q = q->next);
 
    if (q == head)
    {
      //将current插入最前面。
      head = current;
    }
    else
    {
      p->next = current;
    }
    current->next = q;
  }
  return head;
}
 
/*
 * 输出链表结点值。
 */
int PrintLink(LinkList head)
{
  LinkList p;
  for (p = head; p ;p = p->next)
  {
    printf("%-3d ", p->data);
  }
  return 0;
}
 
int main()
{
  LinkList head;
 
  printf("输入Total个数以创建链表：\n");
  head = CreatLink(TOTAL);
   
  head = LinkInsertSort(head);
  printf("排序后：\n");
  PrintLink(head);
  putchar('\n');
  return 0;
}

3. Linked list merge sort

Basic idea: If the linked list If it is empty or contains a node, the linked list is naturally ordered. Otherwise, split the linked list into two parts, merge sort each part separately, and then merge the two sorted linked lists together.

Merge sort code:

/*
 * 链表归并排序(由小到大)。
 * 输入：链表的头指针，
 * 输出：排序后链表的头指针。
 * 递归实现方法：将链表head分为两部分，分别进行归并排序，再将排序后的两部分归并在一起。
 * 递归结束条件：进行递归排序的链表为空或者只有一个结点。
 */
LinkList LinkMergeSort(LinkList head)
{
  LinkList head1, head2;
  if (head == NULL || head->next == NULL)
    return head;
  
  LinkSplit(head, &head1, &head2);
  head1 = LinkMergeSort(head1);
  head2 = LinkMergeSort(head2);
  head = LinkMerge(head1, head2);
  return head;
}

The linked list split function is as follows. The basic idea is to use slow/fast pointers. See the comments for the specific implementation method.

/*
 * 链表分割函数。
 * 将链表head均分为两部分head1和head2，若链表长度为奇数，多出的结点从属于第一部分。
 * 实现方法：首先使指针slow/fast指向链首，
 * 然后使fast指针向前移动两个结点的同时，slow指针向前移动一个结点，
 * 循环移动，直至fast指针指向链尾。结束时，slow指向链表head1的链尾。
 */
int LinkSplit(LinkList head, LinkList *head1, LinkList *head2)
{
  LinkList slow, fast;
  
  if (head == NULL || head->next == NULL)
  {
    *head1 = head;
    *head2 = NULL;
    return 0;
  }
  slow = head;
  fast = head->next;
  while (fast)
  {
    fast = fast->next;
    if (fast)
    {
      fast = fast->next;
      slow = slow->next;
    }
  }
  *head1 = head;
  *head2 = slow->next;
  
  //注意：一定要将链表head1的链尾置空。
  slow->next = NULL;
  return 0;
}

The linked list merge function has two methods: recursive implementation and non-recursive implementation:

Non-recursive implementation:

/*
 * 链表归并。
 * 将两个有序的链表归并在一起，使总链表有序。
 * 输入：链表head1和链表head2
 * 输出：归并后的链表
 * 实现方法：将链表head2中的结点依次插入到链表head1中的适当位置，使head1仍为有序链表。
 */
LinkList LinkMerge(LinkList head1, LinkList head2)
{
  LinkList p, q, t;
  
  if (!head1)
    return head2;
  if (!head2)
    return head1;
  
  //循环变量的初始化，q指向链表head1中的当前结点，p为q的前驱。
  p = NULL;
  q = head1;
  while (head2)
  {
    //t为待插入结点。
    t = head2;
    head2 = head2->next;
    //寻找插入位置，插入位置为p和q之间。
    for (;q && q->data <= t->data; p = q, q = q->next);
    if (p == NULL)
      head1 = t;
    else
      p->next = t;
    t->next = q;
    //将结点t插入到p和q之间后，使p重新指向q的前驱。
    p = t;
  }
  return head1;
}

Recursive implementation:

LinkList LinkMerge2(LinkList head1, LinkList head2)
{
  LinkList result;
  
  if (!head1)
    return head2;
  if (!head2)
    return head1;
  
  if (head1->data <= head2->data)
  {
    result = head1;
    result->next = LinkMerge(head1->next, head2);
  }
  else
  {
    result = head2;
    result->next = LinkMerge(head1, head2->next);
  }
  return result;
}

Complete source code:

/*
* 链表归并排序，由小到大。
*/
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
 
#define TOTAL 10    //链表长度
 
//链表的存储表示
typedef int ElemType;
typedef struct LNode
{
  ElemType data;
  struct LNode *next;
}LNode, *LinkList;
 
LinkList CreatLink(int num);
LinkList LinkMergeSort(LinkList head);
LinkList LinkMerge(LinkList head1, LinkList head2);
LinkList LinkMerge2(LinkList head1, LinkList head2);
int LinkSplit(LinkList head, LinkList *head1, LinkList *head2);
int PrintLink(LinkList head);
 
/*
* 创建链表。
* 形参num为链表的长度，函数返回链表的头指针。
*/
LinkList CreatLink(int num)
{
  int i, data;
 
  //p指向当前链表中最后一个结点，q指向准备插入的结点。
  LinkList head = NULL, p = NULL, q;
 
  for (i = 0; i < num; i++)
  {
    scanf("%d", &data);
    q = (LinkList)malloc(sizeof(LNode));
    q->data = data;
    q->next = NULL;
    if (i == 0)
    {
      head = q;
    }
    else
    {
      p->next = q;
    }
    p = q;
  }
  return head;
}
 
/*
* 输出链表结点值。
*/
int PrintLink(LinkList head)
{
  LinkList p;
  for (p = head; p; p = p->next)
  {
    printf("%-3d ", p->data);
  }
  return 0;
}
 
int main()
{
  LinkList head;
 
  printf("输入Total个数以创建链表：\n");
  head = CreatLink(TOTAL);
 
  head = LinkMergeSort(head);
  printf("排序后：\n");
  PrintLink(head);
  putchar(&#39;\n&#39;);
  return 0;
}
 
/*
 * 链表归并排序(由小到大)。
 * 输入：链表的头指针，
 * 输出：排序后链表的头指针。
 * 递归实现方法：将链表head分为两部分，分别进行归并排序，再将排序后的两部分归并在一起。
 * 递归结束条件：进行递归排序的链表为空或者只有一个结点。
 */
LinkList LinkMergeSort(LinkList head)
{
  LinkList head1, head2;
  if (head == NULL || head->next == NULL)
    return head;
 
  LinkSplit(head, &head1, &head2);
  head1 = LinkMergeSort(head1);
  head2 = LinkMergeSort(head2);
  head = LinkMerge(head1, head2);    //非递归实现
  //head = LinkMerge2(head1, head2);  //递归实现
  return head;
}
 
/*
 * 链表归并。
 * 将两个有序的链表归并在一起，使总链表有序。
 * 输入：链表head1和链表head2
 * 输出：归并后的链表
 * 实现方法：将链表head2中的结点依次插入到链表head1中的适当位置，使head1仍为有序链表。
 */
LinkList LinkMerge(LinkList head1, LinkList head2)
{
  LinkList p, q, t;
 
  if (!head1)
    return head2;
  if (!head2)
    return head1;
 
  //循环变量的初始化，q指向链表head1中的当前结点，p为q的前驱。
  p = NULL;
  q = head1;
  while (head2)
  {
    //t为待插入结点。
    t = head2;
    head2 = head2->next;
    //寻找插入位置，插入位置为p和q之间。
    for (;q && q->data <= t->data; p = q, q = q->next);
    if (p == NULL)
      head1 = t;
    else
      p->next = t;
    t->next = q;
    //将结点t插入到p和q之间后，使p重新指向q的前驱。
    p = t;
  }
  return head1;
}
 
LinkList LinkMerge2(LinkList head1, LinkList head2)
{
  LinkList result;
 
  if (!head1)
    return head2;
  if (!head2)
    return head1;
 
  if (head1->data <= head2->data)
  {
    result = head1;
    result->next = LinkMerge(head1->next, head2);
  }
  else
  {
    result = head2;
    result->next = LinkMerge(head1, head2->next);
  }
  return result;
}
 
/*
 * 链表分割函数。
 * 将链表head均分为两部分head1和head2，若链表长度为奇数，多出的结点从属于第一部分。
 * 实现方法：首先使指针slow/fast指向链首，
 * 然后使fast指针向前移动两个结点的同时，slow指针向前移动一个结点，
 * 循环移动，直至fast指针指向链尾。结束时，slow指向链表head1的链尾。
 */
int LinkSplit(LinkList head, LinkList *head1, LinkList *head2)
{
  LinkList slow, fast;
 
  if (head == NULL || head->next == NULL)
  {
    *head1 = head;
    *head2 = NULL;
    return 0;
  }
  slow = head;
  fast = head->next;
  while (fast)
  {
    fast = fast->next;
    if (fast)
    {
      fast = fast->next;
      slow = slow->next;
    }
  }
  *head1 = head;
  *head2 = slow->next;
 
  //注意：一定要将链表head1的链尾置空。
  slow->next = NULL;
  return 0;
}

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