**Cycle Detection**

### Problem Statement :

A linked list is said to contain a cycle if any node is visited more than once while traversing the list. Given a pointer to the head of a linked list, determine if it contains a cycle. If it does, return 1. Otherwise, return 0. Example head refers 1 -> 2 -> 3 -> NUL The numbers shown are the node numbers, not their data values. There is no cycle in this list so return 0. head refers 1 -> 2 -> 3 -> 1 -> NULL There is a cycle where node 3 points back to node 1, so return 1. Function Description Complete the has_cycle function in the editor below. It has the following parameter: SinglyLinkedListNode pointer head: a reference to the head of the list Returns int: 1 if there is a cycle or 0 if there is not Note: If the list is empty, head will be null. Input Format The code stub reads from stdin and passes the appropriate argument to your function. The custom test cases format will not be described for this question due to its complexity. Expand the section for the main function and review the code if you would like to figure out how to create a custom case.

### Solution :

` ````
Solution in C :
In C++ :
/*
Detect loop in a linked list
List could be empty also
Node is defined as
struct Node
{
int data;
struct Node *next;
}
*/
int HasCycle(Node* head)
{
// Complete this function
// Do not write the main method
Node *slowp = head, *fastp = head;
while (slowp && fastp && fastp->next)
{
slowp = slowp->next;
fastp = fastp->next->next;
if (slowp == fastp)
{
return 1;
}
}
return 0;
}
In Java :
/*
Insert Node at the end of a linked list
head pointer input could be NULL as well for empty list
Node is defined as
class Node {
int data;
Node next;
}
*/
int HasCycle(Node head) {
if(head==null)
return 0;
if(head.next==head)
return 1;
Node slow=head;
Node fast=head;
while(fast!=null)
{
fast=fast.next;
if(fast!=null)
fast=fast.next;
else
return 0;
slow=slow.next;
if(slow==fast)
return 1;
}
return 0;
}
In C :
// Complete the has_cycle function below.
/*
* For your reference:
*
* SinglyLinkedListNode {
* int data;
* SinglyLinkedListNode* next;
* };
*
*/
bool has_cycle(SinglyLinkedListNode* head) {
struct SinglyLinkedListNode* slow=head, * fast=head;
while((slow!=NULL)&&(fast!=NULL)&&(fast->next!=NULL))
{
slow=slow->next;
fast=fast->next->next;
if(slow==fast)
return 1;
}
return 0;
}
In python3 :
"""
Check if linked list has cycle
head could be None as well for empty list
Node is defined as
class Node(object):
def __init__(self, data=None, next_node=None):
self.data = data
self.next = next_node
return 0 if no cycle else return 1
"""
def HasCycle(head):
slow = head
fast = head.next
count = 0
while slow and fast and count==0:
if slow == fast:
count=1
else:
slow= slow.next
fast = fast.next.next
if fast !=None or count == 1:
return(1)
else:
return(0)
```

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