The old "tortoise and the hare" problem. Essentially, the "fast" pointer moves 2x the speed as the "slow" pointer. If there is a cycle, they will meet.

int HasCycle(Node head) {
    if (head == null){
        return 0;
    }

    Node slow = head;
    Node fast = head;

    while (fast != null && fast.next != null){
        slow = slow.next;
        fast = fast.next.next;

        if (slow == fast){
            return 1;
        }
    }

    return 0;
}

The predefined codes in Java 7, Javascript, Python 2, Python 3 are not working!

I took two pointers from head. Increased one pointer by 2 with every iteration and another pointer with 1. If there is loop they will somehow meet in the loop and will return 1. If any of them encounters NULL return 0 :)

Problem solving this exercise the main function contains "int" declaration on javascript code making fail the execution

function main() {
    ....

    for (let testsItr = 0; testsItr < tests; testsItr++) {
        ....

        for (int i = 0; i < llistCount; i++) {
          	if (i == index) {
            	extra = temp;
          	}

          	if (i != llistCount-1) {
            	temp = temp.next;
          	}
        }
        ....
}

Could you fix this issue or tell me where I can submit a pull request to solve it? Thanks

Can someone please explain the input 1, and the output 01101. I understand that there are 5 linked list given as input, and each input integer in output says whether the corresponding lined ist has cycle or not. I am getting output 01111. can any of the moderator give the 4th input linked list. It would be helpful in debugging.