// Runtime: 0 ms, faster than 100.00% of Java online submissions for Linked List Cycle.
public class Solution {
    public boolean hasCycle(ListNode head) {
        if (head == null) return false;
        ListNode start = head;

        int steps = 1;
        for (;;) {
            ListNode next = start;

            for (int i = 0; i < steps; i++) {
                next = next.next;
                if (next == null) return false;
                if (next == start) return true;
            }

            start = next;
            steps *= 2;
        }
    }
}