cycle_detecting.java

public class cycle_detecting {
        public static class Node{
        Node next;

        public Node(int data){
            this.next = null;
        }
    }

    public static Node head;

    // cycle detecting
    public static boolean isCycle(){ //floyd's cycle detecting algorithm
        Node slow = head;
        Node fast = head;

        while (fast != null && fast.next != null) {
            slow = slow.next; //+1
            fast = fast.next.next; //+2
            if (slow == fast) {
                return true; // cycle exists
            }
        }

        return false; // cycle doesn't exist
    }

    // remove cycle (agar head se connect nhi karna hai)
    public static void removeCycle(){
        // detect cycle
        Node slow = head;
        Node fast = head;
        boolean cycle = false;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
            if (fast == slow) {
                cycle = true;
                break;
            }
        }

        if (cycle == false) {
            return;
        }

        // find meeting point
        slow = head;
        Node prev = null; // last node
        while (slow != fast) {
            prev = fast;
            slow = slow.next;
            fast = fast.next;
        }

        //remove cycle -> last.next = null
        prev.next = null;
        
    }

    public static void main(String[] args) {
        head = new Node(1);
        Node temp = new Node(2);
        head.next = temp;
        head.next.next = new Node(3);
        head.next.next.next = temp;

        // 1->2->3->2
        System.out.println(isCycle());
        removeCycle();
        System.out.println(isCycle());
    }
}