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

struct _listNode{
    int item;
    struct _listNode* next;
};
typedef struct _listNode ListNode;

void printList(ListNode *head);
void deleteList(ListNode **ptrHead);
int checkNext (ListNode *head, int K);
void reverseKNodes(ListNode** head, int K);

int main()
{
    ListNode *head = NULL, *temp;
	int i = 0;
	int K = 0;

	scanf("%d",&K);

	while (scanf("%d", &i)){
		if (head == NULL){
			head = (ListNode*) malloc(sizeof(ListNode));
			temp = head;
		}
		else{
			temp->next = (ListNode*) malloc(sizeof(ListNode));
			temp = temp->next;
		}
		temp->item = i;
	}
	temp->next = NULL;


	reverseKNodes(&head, K);
	printList(head);
    deleteList(&head);
	return 0;
}

void printList(ListNode *head){
    while(head !=NULL){
        printf("%d ",head->item);
        head = head->next;
    }
    printf("\n");
}
void deleteList(ListNode **ptrHead){
    ListNode *cur = *ptrHead;
    ListNode *temp;
    while (cur!= NULL) {
		temp=cur->next;
		free(cur);
		cur=temp;
	}
	*ptrHead=NULL;
}

void reverseKNodes(ListNode** head, int K)
{
    int check = checkNext(*head, K);
    ListNode *cur, *after, *prev, *temp, *tail, *start;
    cur = *head;
    temp = *head;
    prev = NULL;

    if (*head == NULL || K<=0) return;

    if (check)
    {
        for (int i=0; i<K; i++)
        {
            after = cur->next;
            cur->next = prev;
            prev = cur;
            cur = after;
        }
        (*head)->next = cur;
        tail = *head;
        *head = prev;
        check = checkNext(cur, K);
        while (check)
        {
            prev = NULL;
            start = cur;
            for (int i=0; i<K; i++)
            {
                after = cur->next;
                cur->next = prev;
                prev = cur;
                cur = after;
            }
            tail->next = prev;
            tail = start;
            check = checkNext(cur, K);
        }
    }
    if (cur != NULL) {
        tail->next = cur;
    } else {
        tail->next = NULL;
    }

    return;

}

int checkNext (ListNode *head, int K) {
    ListNode *temp = head;
    while (K>0) {
        if (temp == NULL) return 0;
        else {
            temp = temp->next;
        }
        K--;
    } return 1;
}

C Language online compiler

Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!

Read inputs from stdin

OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}