how to move nodes from begining to the end in linked list? C

Question

i want to build a program which takes K elements from the begining of the linked list and putting them in the end of the linked link, kinda spin. for example : if there is linked list : 1->2->3->4->5 and k = 2 then the linked list will look like that : 3->4->5->1->2 here is my try, please help me:

void spinfunc(struct node *node_ptr)
{
    int k = 0;
    int count = 0;
    int temp;
    printf("enter a number of the lements from the begin to be deleted - ");
    scanf("%d", &k);
    while (node_ptr != NULL)
    {
        if (count + 1 <= k)
        {
            count++;
            printf("count: %d", count);
            temp = node_ptr->data;
            node_ptr->data = NULL;
        }
        node_ptr = node_ptr->next;
    }
    printf("%d ", temp);

}

Answer 1

It can be done in a more simple steps.

We only need to change the next pointer of kth node and tail node of list i.e.

kth node -> next = null
tail node -> next = head

And then update the head to (k+1)th node.

Overall logic:

Traverse the list from beginning and stop at kth node. Store pointer to kth node. We can get (k+1)th node using kthNode->next. Keep traversing till end and store pointer to last node also. Finally, change pointers as stated above.

struct node* spinFunc(struct node *head)

{

int k = 2; //assuming k = 2 
// list = 1->2->3->4->5.
struct node* current = head;
struct node* newHead = NULL;

int count = 1;
while (count < k && current != NULL)
{
    current = current->next;
    count++;
}
//Now current is pointing to node 2 

// current points to kth node. Store it in a variable.
struct node *kthNode = current;

// current will point to last node i.e. node 5 after this loop
while (current->next != NULL)
    current = current->next;

//last node -> next = head
current->next = head;

//update the head now
newHead = kthNode -> next;

kthNode->next = NULL;

//return the new head
return newHead;

}