Java Solution (12 ms) using HashSet

  • 0

    If you're allowed to use extra space, this is a pretty concise way to do it.

    public boolean hasCycle(ListNode head) {
        HashSet<ListNode> hashSet = new HashSet<>();
        while(head != null) {
            if(hashSet.contains(head)) return true;
            head =;
        return false;

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