141. Linked List Cycle

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Total Accepted: 177986
Total Submissions: 502453
Difficulty: Easy
Contributor: LeetCode

Given a linked list, determine if it has a cycle in it.
Follow up:Can you solve it without using extra space?

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Linked List Two Pointers
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(M) Linked List Cycle II

    /*
      Use two pointers, slower and faster.
        slower moves step by step. faster moves two steps at time.
        if the Linked List has a cycle slower and faster will meet at some
        point.
    */
    public boolean hasCycle(ListNode head) {
        ListNode slow = new ListNode(0);
        ListNode fast = new ListNode(0);
        slow.next = head;
        fast.next = head;
        
        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
             if (fast == slow) {
                return true;
            }
        }
        return false;
    }