C語言刪除回圈連結串列中的資料項程式

建立一個迴圈連結串列，並刪除回圈連結串列中的資料項的範例程式，將以下程式碼儲存到一個原始檔中：remove_item_in_circular_linked_list.c， 如下所示 -

#include <stdio.h>
#include <stdlib.h>

struct node {
    int data;
    struct node *next;
};

struct node *head = NULL;
struct node *current = NULL;
struct node *prev = NULL;

//insert link at the first location
void insert(int data) {
    // Allocate memory for new node;
    struct node *link = (struct node*) malloc(sizeof(struct node));

    link->data = data;
    link->next = NULL;

    // If head is empty, create new list
    if (head == NULL) {
        head = link;
        head->next = link;
        return;
    }

    current = head;

    // move to the end of the list
    while (current->next != head)
        current = current->next;

    // Insert link at the end of the list
    current->next = link;

    // Link the last node back to head
    link->next = head;

}

void remove_data(int data) {
    int pos = 0;

    if (head == NULL) {
        printf("Linked List not initialized");
        return;
    }

    if (head->data == data) {
        if (head->next != head) {
            current = head;
            while (current->next != head) {
                current = current->next;
            }
            current->next = head->next;
            head = head->next;
            return;
        }
        else {
            head = NULL;
            printf("List is empty\n");
            exit(0);
        }
    }
    else if (head->data != data && head->next == NULL) {
        printf("%d not found in the list\n", data);
        return;
    }


    current = head;

    while (current->next != head && current->data != data) {
        prev = current;
        current = current->next;
    }

    if (current->data == data) {
        prev->next = prev->next->next;
        free(current);
    }
    else
        printf("%d not found in the list.", data);
}

//display the list
void printList() {
    struct node *ptr = head;

    printf("\n[head] =>");

    //start from the beginning
    while (ptr->next != head) {
        printf(" %d =>", ptr->data);
        ptr = ptr->next;
    }

    printf(" %d =>", ptr->data);
    printf(" [head]\n");
}

int main() {
    insert(10);
    insert(20);
    insert(30);
    insert(40);
    insert(50);
    insert(60);

    printf("Original List -");
    printList();
    remove_data(20);

    printf("List after removal -");
    printList();

    return 0;
}

執行上面程式，得到以下結果 -

Original List -
[head] => 10 => 20 => 30 => 40 => 50 => 60 => [head]
List after removal -
[head] => 10 => 30 => 40 => 50 => 60 => [head]