Code:
#include stdio.h
#include stdlib.h
struct node
{
int num;
struct node *next;
};
void create(struct node **);
void makecycle(struct node **);
void release(struct node **);
int detectcycle(struct node *);
int main()
{
struct node *p = NULL;
int result;
printf("Enter data into the list\n");
create(&p);
makecycle(&p); //comment it to avoid cycle creation
printf("Identifying if a cycle exists.\n");
result = detectcycle(p);
if (result)
{
printf("Cycle detected in the linked list.\n");
}
else
{
printf("No cycle detected in the linked list.\n");
}
release (&p);
return 0;
}
void makecycle(struct node **p)
{
struct node *rear, *front;
int n, count = 0, i;
front = rear = *p;
while (rear->next != NULL)
{
rear = rear->next;
count++;
}
if (count)
{
n = rand() % count;
}
else
{
n = 1;
}
for (i = 0; i < n - 1; i++)
{
front = front->next;
}
rear->next = front;
/*At this point a cycle is generated in the list*/
}
int detectcycle(struct node *head)
{
int flag = 1, count = 1, i;
struct node *p, *q;
p = q = head;
q = q->next;
while (1)
{
q = q->next;
if (flag)
{
p = p->next;
}
if (q == p)
{
/*Deleting the loop to deallocate the list*/
q = q->next;
while (q != p)
{
count++;
q = q->next;
}
q = p = head;
for (i = 0; i < count; i++)
{
q = q->next;
}
while (p != q)
{
p = p->next;
q = q->next;
}
q->next = NULL;
return 1;
}
else if (q->next == NULL)
{
return 0;
}
flag = !flag;
}
}
void create(struct node **head)
{
int c, ch;
struct node *temp, *rear;
do
{
printf("Enter number: ");
scanf("%d", &c);
temp = (struct node *)malloc(sizeof(struct node));
temp->num = c;
temp->next = NULL;
if (*head == NULL)
{
*head = temp;
}
else
{
rear->next = temp;
}
rear = temp;
printf("Do you wish to continue [1/0]: ");
scanf("%d", &ch);
} while (ch != 0);
printf("\n");
}
void release(struct node **head)
{
struct node *temp = *head;
temp = temp->next;
while ((*head) != NULL)
{
free(temp);
temp = *head;
(*head) = (*head)->next;
}
}
Output:
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
Identifying if a cycle exists.
Cycle detected in the linked list..
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