LeetCode_Algorithms_141_Linked_List_Cycle_Impl2.cs

public bool HasCycle(ListNode head)
{
    // case of 0 or 1 node
    if (head == null || head.next == null)
        return false;

    ListNode slowPtr = head;
    ListNode fastPtr = head.next;
    while (fastPtr != slowPtr && fastPtr.next != slowPtr)
    {
        // fastPtr走訪到盡頭代表無cycle
        if (fastPtr.next == null || fastPtr.next.next == null)
            return false;
        slowPtr = slowPtr.next;
        fastPtr = fastPtr.next.next;
    }
    return true;
}