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.

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

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 */
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#include <stdio.h>
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#include <stdlib.h>
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```
 
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```
struct node
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{
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    int num;
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    struct node *next;
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};
```
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void create(struct node **);
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void reverse(struct node **, int);
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void release(struct node **);
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void display(struct node *);
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int main()
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{
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    struct node *p = NULL;
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    int n;
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    printf("Enter data into the list\n");

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    create(&p);
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    printf("Displaying the nodes in the list:\n");

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    display(p);
```

    printf("Enter the number N to reverse first N node: ");

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

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    display(p);
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    release(&p);
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    return 0;
```
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}
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```
 
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void reverse(struct node **head, int n)
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{
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    struct node *p, *q, *r, *rear;
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    p = q = r = *head;
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    if (n == 0)
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    {
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        q = q->next;
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        p->next = q->next;
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        q->next = p;
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        *head = q;
```
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    }
```
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    else
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```
    {
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        p = p->next->next;
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        q = q->next;
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        r->next = NULL;
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        rear = r;
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        q->next = r;
```
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        while (n > 0 && p != NULL)
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        {
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            r = q;
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            q = p;
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            p = p->next;
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            q->next = r;
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            n--;
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        }
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        *head = q;
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        rear->next = p;
```
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    }
```
```
}
```
```
 
```
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void create(struct node **head)
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```
{
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    int c, ch;
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    struct node *temp, *rear;
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```
 
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    do
```
```
    {
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        printf("Enter number: ");
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        scanf("%d", &c);
```

        temp = (struct node *)malloc(sizeof(struct node));

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        temp->num = c;
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        temp->next = NULL;
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        if (*head == NULL)
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        {
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            *head = temp;
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        }
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        else
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```
        {
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            rear->next = temp;
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        }
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        rear = temp;
```

        printf("Do you wish to continue [1/0]: ");

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        scanf("%d", &ch);
```
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    } while (ch != 0);
```
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    printf("\n");
```
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}
```
```
 
```
```
void display(struct node *p)
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```
{
```
```
    while (p != NULL)
```
```
    {
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        printf("%d\t", p->num);
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        p = p->next;
```
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    }
```
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    printf("\n");
```
```
}
```
```
 
```
```
void release(struct node **head)
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```
{
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    struct node *temp = *head;
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    *head = (*head)->next;
```
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    while ((*head) != NULL)
```
```
    {
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        free(temp);
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        temp = *head;
```
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        (*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