C Program to Reverse First N Elements of a Linked List

This C Program to reverse only first N elements of a linked list.

Here is a source code of the C Program that reverses only first n elements of a linked list. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C Program to Reverse only First N Elements of a Linked List

```
 */
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
struct node
```
```
{
```
```
    int num;
```
```
    struct node *next;
```
```
};
```
```
 
```
```
void create(struct node **);
```
```
void reverse(struct node **, int);
```
```
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("Enter the number N to reverse first N node: ");

```
    scanf("%d", &n);
```
```
    printf("Reversing the list...\n");
```
```
    if (n > 1)
```
```
    {
```
```
        reverse(&p, n - 2);
```
```
    }
```

    printf("Displaying the reversed list:\n");

```
    display(p);
```
```
    release(&p);
```
```
 
```
```
    return 0;
```
```
}
```
```
 
```
```
void reverse(struct node **head, int n)
```
```
{
```
```
    struct node *p, *q, *r, *rear;
```
```
 
```
```
    p = q = r = *head;
```
```
    if (n == 0)
```
```
    {
```
```
        q = q->next;
```
```
        p->next = q->next;
```
```
        q->next = p;
```
```
        *head = q;
```
```
    }
```
```
    else
```
```
    {
```
```
        p = p->next->next;
```
```
        q = q->next;
```
```
        r->next = NULL;
```
```
        rear = r;
```
```
        q->next = r;
```
```
 
```
```
        while (n > 0 && p != NULL)
```
```
        {
```
```
            r = q;
```
```
            q = p;
```
```
            p = p->next;
```
```
            q->next = r;
```
```
            n--;
```
```
        }
```
```
        *head = q;
```
```
        rear->next = p;
```
```
    }
```
```
}
```
```
 
```
```
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;
```
```
    }
```
```
}
```

$ cc nreverse.c 
$ ./a.out 
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]: 1
Enter number: 6
Do you wish to continue [1/0]: 1
Enter number: 7
Do you wish to continue [1/0]: 0
 
Displaying the nodes in the list:
1	2	3	4	5	6	7	
Enter the number N to reverse first N node: 4
Reversing the list...
Displaying the reversed list:
4	3	2	1	5	6	7

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