Answer by Ashok Bijoy Debnath for How to detect a loop in a linked list?

Better than Floyd's algorithm

Richard Brent described an alternative cycle detection algorithm, which is pretty much like the hare and the tortoise [Floyd's cycle] except that, the slow node here doesn't move, but is later "teleported" to the position of the fast node at fixed intervals.

The description is available here : http://www.siafoo.net/algorithm/11 Brent claims that his algorithm is 24 to 36 % faster than the Floyd's cycle algorithm. O(n) time complexity, O(1) space complexity.

public static boolean hasLoop(Node root){
    if(root == null) return false;

    Node slow = root, fast = root;
    int taken = 0, limit = 2;

    while (fast.next != null) {
        fast = fast.next;
        taken++;
        if(slow == fast) return true;

        if(taken == limit){
            taken = 0;
            limit <<= 1;    // equivalent to limit *= 2;
            slow = fast;    // teleporting the turtle (to the hare's position) 
        }
    }
    return false;
}