C语言基础（二十二）

在C语言中，对链表进行排序涉及到比较链表中的节点值，并根据比较结果重新排列这些节点。由于链表是非连续存储的数据结构，其排序比数组排序要复杂一些。由链表的结构特性可知，插入排序和归并排序更适合链表排序。

测试代码1：

cpp 复制代码

#include "date.h"
#include <stdio.h>  
#include <stdlib.h>  
  
// 定义链表节点的结构体  
typedef struct ListNode {  
    int value;  
    struct ListNode* next;  
} ListNode;  
  
// 创建一个新节点  
ListNode* createNode(int value) {  
    ListNode* newNode = (ListNode*)malloc(sizeof(ListNode));  
    if (newNode == NULL) {  
        printf("Memory allocation failed!\n");  
        exit(1);  
    }  
    newNode->value = value;  
    newNode->next = NULL;  
    return newNode;  
}  
  
// 在链表末尾添加一个新节点  
void appendNode(ListNode** head, int value) {  
    ListNode* newNode = createNode(value);  
    if (*head == NULL) {  
        *head = newNode;  
    } else {  
        ListNode* current = *head;  
        while (current->next != NULL) {  
            current = current->next;  
        }  
        current->next = newNode;  
    }  
}  
  
// 在链表头部插入一个新节点  
void insertNodeAtHead(ListNode** head, int value) {  
    ListNode* newNode = createNode(value);  
    newNode->next = *head;  
    *head = newNode;  
}  
  
// 删除链表中值为value的节点（只删除第一个找到的）  
void deleteNode(ListNode** head, int value) {  
    ListNode *temp = *head, *prev = NULL;  
    if (temp != NULL && temp->value == value) {  
        *head = temp->next;  
        free(temp);  
        return;  
    }  
    while (temp != NULL && temp->value != value) {  
        prev = temp;  
        temp = temp->next;  
    }  
    if (temp == NULL) return;  
    prev->next = temp->next;  
    free(temp);  
}  
  
// 归并两个已排序的链表  
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {  
    ListNode* dummyHead = (ListNode*)malloc(sizeof(ListNode));  
    ListNode* tail = dummyHead;  
    dummyHead->next = NULL;  
  
    while (l1 && l2) {  
        if (l1->value < l2->value) {  
            tail->next = l1;  
            l1 = l1->next;  
        } else {  
            tail->next = l2;  
            l2 = l2->next;  
        }  
        tail = tail->next;  
    }  
  
    tail->next = (l1 != NULL) ? l1 : l2;  
  
    ListNode* sortedList = dummyHead->next;  
    free(dummyHead); // 释放dummyHead的内存  
    return sortedList;  
}  
  
// 链表归并排序  
ListNode* sortList(ListNode* head) {  
    if (!head || !(head->next)) {  
        return head;  
    }  
  
    // 使用快慢指针找到链表的中间节点  
    ListNode *slow = head, *fast = head, *prev = NULL;  
    while (fast && fast->next) {  
        prev = slow;  
        slow = slow->next;  
        fast = fast->next->next;  
    }  
  
    // 分割链表  
    prev->next = NULL;  
  
    // 递归排序两半，然后合并  
    ListNode *left = sortList(head);  
    ListNode *right = sortList(slow);  
    return mergeTwoLists(left, right);  
}
// 遍历链表并打印节点值  
void printList(ListNode* head) {  
    ListNode* current = head;  
    while (current != NULL) {  
        printf("%d -> ", current->value);  
        current = current->next;  
    }  
    printf("NULL\n");  
}  
  
// 释放链表占用的内存  
void freeList(ListNode* head) {  
    ListNode* temp;  
    while (head != NULL) {  
        temp = head;  
        head = head->next;  
        free(temp);  
    }  
}  
  
int main() {  

    int time = getTime();
    ListNode* head = NULL;  
  
    // 向链表添加数据 
    appendNode(&head, 3);  
    appendNode(&head, 1);  
    appendNode(&head, 4);  
    appendNode(&head, 8);  
    appendNode(&head, 5);  
    appendNode(&head, 9);  
  
    // 打印原始链表  
    printf("Original list: ");  
    printList(head);  
  
    // 在链表头部插入节点  
    insertNodeAtHead(&head, 0);  
    printf("After inserting 0 at head: ");  
    printList(head);  
  
    // 删除值为1的节点（只删除第一个）  
    deleteNode(&head, 0);  
    printf("After deleting the first 1: ");  
    printList(head);  
  
    // 对链表进行排序  
    head = sortList(head);  
    printf("Sorted list: ");  
    printList(head);  
  
    // 释放链表内存  
    freeList(head);  
  
    return 0;  
}

运行结果如下：

测试代码2：

cpp 复制代码

#include "date.h"
#include <stdio.h>  
#include <stdlib.h>  
  
typedef struct Node {  
    int data;  
    struct Node* next;  
} Node;  
  
Node* createNode(int data) {  
    Node* newNode = (Node*)malloc(sizeof(Node));  
    if (!newNode) {  
        printf("Memory allocation failed\n");  
        exit(1);  
    }  
    newNode->data = data;  
    newNode->next = NULL;  
    return newNode;  
}  
  
void appendNode(Node** head, int data) {  
    Node* newNode = createNode(data);  
    if (*head == NULL) {  
        *head = newNode;  
    } else {  
        Node* current = *head;  
        while (current->next != NULL) {  
            current = current->next;  
        }  
        current->next = newNode;  
    }  
}  
  
void printList(Node* head) {  
    Node* current = head;  
    while (current != NULL) {  
        printf("%d -> ", current->data);  
        current = current->next;  
    }  
    printf("NULL\n");  
}  
  
void insertionSortList(Node** headRef) {  
    Node* sorted = NULL; // 已排序链表的头指针  
    Node* current = *headRef; // 当前未排序链表的头指针  
    Node* next;  
  
    // 当未排序链表非空时  
    while (current != NULL) {  
        next = current->next; // 保存当前节点的下一个节点  
  
        // 在已排序链表中找到插入位置  
        Node* prev = NULL;  
        Node* sortedCurrent = sorted;  
        while (sortedCurrent != NULL && sortedCurrent->data < current->data) {  
            prev = sortedCurrent;  
            sortedCurrent = sortedCurrent->next;  
        }  
  
        // 插入到已排序链表中  
        current->next = sortedCurrent;  
        if (prev == NULL) {  
            sorted = current; // 插入到已排序链表的头部  
        } else {  
            prev->next = current;  
        }  
  
        // 处理下一个未排序的节点  
        current = next;  
    }  
  
    // 更新原始链表的头指针为已排序链表的头指针  
    *headRef = sorted;  
}  
  
void freeList(Node* head) {  
    Node* temp;  
    while (head != NULL) {  
        temp = head;  
        head = head->next;  
        free(temp);  
    }  
}  
  
int main() {  
    int time = getTime();
    Node* head = NULL;  
  
    appendNode(&head, 4);  
    appendNode(&head, 2);  
    appendNode(&head, 5);  
    appendNode(&head, 1);  
    appendNode(&head, 3);  
  
    printf("Original list: ");  
    printList(head);  
  
    insertionSortList(&head);  
  
    printf("Sorted list: ");  
    printList(head);  
  
    freeList(head);  
  
    return 0;  
}

运行结果如下：