Using Python
class ListNode:
def __init__(self, val):
self.val = val
self.next = None
def has_cycle(head):
slow = head
fast = head
while fast is not None and fast.next is not None:
slow = slow.next
fast = fast.next.next
if slow == fast:
return True
return False
# Creating a linked list with a loop
head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(3)
head.next.next.next = ListNode(4)
head.next.next.next.next = ListNode(5)
head.next.next.next.next.next = head.next # Creating a loop
print("Has cycle:", has_cycle(head))
Using Java
class ListNode {
int val;
ListNode next;
ListNode(int val) {
this.val = val;
this.next = null;
}
}
public class LinkedListCycle {
public boolean hasCycle(ListNode head) {
if (head == null || head.next == null) {
return false;
}
ListNode slow = head;
ListNode fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
return true;
}
}
return false;
}
public static void main(String[] args) {
ListNode head = new ListNode(1);
head.next = new ListNode(2);
head.next.next = new ListNode(3);
head.next.next.next = new ListNode(4);
head.next.next.next.next = new ListNode(5);
head.next.next.next.next.next = head.next; // Creating a loop
LinkedListCycle cycleDetector = new LinkedListCycle();
System.out.println("Has cycle: " + cycleDetector.hasCycle(head));
}
}
Using C
#include <stdio.h>
#include <stdbool.h>
struct ListNode {
int val;
struct ListNode* next;
};
bool hasCycle(struct ListNode* head) {
if (head == NULL || head->next == NULL) {
return false;
}
struct ListNode* slow = head;
struct ListNode* fast = head;
while (fast != NULL && fast->next != NULL) {
slow = slow->next;
fast = fast->next->next;
if (slow == fast) {
return true;
}
}
return false;
}
int main() {
struct ListNode* head = (struct ListNode*)malloc(sizeof(struct ListNode));
head->val = 1;
head->next = (struct ListNode*)malloc(sizeof(struct ListNode));
head->next->val = 2;
head->next->next = (struct ListNode*)malloc(sizeof(struct ListNode));
head->next->next->val = 3;
head->next->next->next = (struct ListNode*)malloc(sizeof(struct ListNode));
head->next->next->next->val = 4;
head->next->next->next->next = (struct ListNode*)malloc(sizeof(struct ListNode));
head->next->next->next->next->val = 5;
head->next->next->next->next->next = head->next; // Creating a loop
printf("Has cycle: %s\n", hasCycle(head) ? "true" : "false");
return 0;
}