Sunday, 12 November 2017

C Program to Reverse a Linked List


Code:

#include   stdio.h
#include   stdlib.h

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

void create(struct node **);
void reverse(struct node **);
void release(struct node **);
void display(struct node *);

int main()
{
    struct node *p = NULL;
    int n;

    printf("Enter data into the list\n");
    create(&p);
    printf("Displaying the nodes in the list:\n");
    display(p);
    printf("Reversing the list...\n");
    reverse(&p);
    printf("Displaying the reversed list:\n");
    display(p);
    release(&p);

    return 0;
}

void reverse(struct node **head)
{
    struct node *p, *q, *r;

    p = q = r = *head;
    p = p->next->next;
    q = q->next;
    r->next = NULL;
    q->next = r;

    while (p != NULL)
    {
        r = q;
        q = p;
        p = p->next;
        q->next = r;
    }
    *head = q;
}

void create(struct node **head)
{
    int c, ch;
    struct node *temp, *rear;

    do
    {
        printf("Enter number: ");
        scanf("%d", &c);
        temp = (struct node *)malloc(sizeof(struct node));
        temp->num = c;
        temp->next = NULL;
        if (*head == NULL)
        {
            *head = temp;
        }
        else
        {
            rear->next = temp;
        }
        rear = temp;
        printf("Do you wish to continue [1/0]: ");
        scanf("%d", &ch);
    } while (ch != 0);
    printf("\n");
}

void display(struct node *p)
{
    while (p != NULL)
    {
        printf("%d\t", p->num);
        p = p->next;
    }
    printf("\n");
}

void release(struct node **head)
{
    struct node *temp = *head;
    *head = (*head)->next;
    while ((*head) != NULL)
    {
        free(temp);
        temp = *head;
        (*head) = (*head)->next;
    }
}


Output:

Enter data into the list
Enter number: 1
Do you wish to continue [1/0]: 1
Enter number: 2
Do you wish to continue [1/0]: 1
Enter number: 3
Do you wish to continue [1/0]: 1
Enter number: 4
Do you wish to continue [1/0]: 1
Enter number: 5
Do you wish to continue [1/0]: 0

Displaying the nodes in the list:
1 2 3 4 5
Reversing the list...
Displaying the reversed list:
5 4 3 2 1


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