Reverse links of K-th order in Linked List

 

/* Explanation

write a program to given a linked list and input k

10->20->30->40->50->60->70->80->90->100

if k=2

output: 20->10->40->30->60->50->80->70->100->90

if k=3

output:30->20->10->60->50->40->90->80->70->100

if k=4

output:40->30->20->10->80->70->60->50->100->90

*/

/*Code*/

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

typedef struct node
{
    int key;
    struct node *next;
}NODE;

void print_link(NODE *p);
void reverse_link(NODE **root);
main()
{
NODE *root=NULL,*p,*q,*r,*s;
int key,i,iteration;

    printf("Enter Numbers and -9999 to end\n");
    do
    {
        scanf("%d",&key);
        if(key == -9999)
        {
            break;
        }
        else
        {
            p= (NODE *)malloc(sizeof(NODE));
            p->key = key;
            p->next = NULL;
            q = root;
            if(q==NULL)
            {
                root = p;
            }
            else
            {
                while (q->next !=NULL)
                {
                    q=q->next;
                }
            q->next = p;
            }
        }
    }while(1);
    printf("Enter K \n");
    scanf("%d",&key);
     printf("original\n");
    print_link(root);
    p = root;
    iteration =1;

    while(p!=NULL && key>=1)
    {
        q=p;
        for(i=0;i<key-1 && p->next!=NULL;i++)
        {
            p=p->next;
        }
        if(iteration == 1)
        {
            root = p;
            iteration++;
        }
        else
        {
            s->next = p;
        }
        r = p->next;
        p->next = NULL;
        s=q;
        reverse_link(&q);
       
        p=r;
    }
    s->next = p;

      
    printf("reversed \n");
    print_link(root);

}

void print_link(NODE *p)
{
    while(p!=NULL)
    {
        printf("%d ",p->key);
        p=p->next;
    }
    printf("\n");
    return;
}
void reverse_link(NODE **root)
{
    NODE *p,*q,*r=NULL;

    if(*root == NULL)
        return;

    p=*root;

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