Question

Code in C only

Need to write a function that when passed a linked list swaps the second and third nodes.

if there are only two nodes then swap them, if one or less nothing happens. and include a drawing showing how it is processed.

Answer 1

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

struct ListNode

{

int value;

struct ListNode *next;

};

void append(struct ListNode** head_ref, int new_data)

{

struct ListNode* new_node = (struct ListNode* ) malloc(sizeof(struct ListNode));

new_node->value = new_data;

struct ListNode *last = *head_ref;

if (*head_ref == NULL)

{

*head_ref = new_node;

return;

}

while (last->next != NULL)

last = last->next;

last->next = new_node;

return;

}

void printList(struct ListNode *node)

{

if(node == NULL){

printf("List is Empty ");

return;

}

int count = 0;

while (node != NULL)

{

if(node->next!=NULL && node->next->value !=10)

printf("%d-->",node->value);

else

printf("%d",node->value);

node = node->next;

}

}

void swap(struct ListNode **node)

{

if(node == NULL || (*node)->next ==NULL){

return;

}

int count = 0;

struct ListNode *first = *node;

struct ListNode *second = first->next;

if(second->next==NULL){

*node = second;

(*node)->next = first;

first->next= NULL;

}else{

struct ListNode *third = second->next;

first->next = third;

second->next = third->next;

third->next = second;

}

}

int main()

{

struct ListNode* head = NULL;

int arr[] = {1,2,3,4, 5};

int i;

for(i = 0; i<5;++i)

append(&head, arr[i]);

printf("List before: ");

printList(head);

swap(&head);

printf(" List after: ");

printList(head);

return 0;

}

=======================================================================
SEE Output


Thanks, PLEASE COMMENT if there is any concern.



Drawing

How it happens is

1 --->2-->3--->4--->5

Now first points to NODE 1
Now SECOND points to NODE 2
Now THIRD points to NODE 3

We swap Node 2 and 3 by changing first next pointer , pointing to third and
Third next pointer pointing to second
second next pointer pointing to third next