public static LeetCode142Node DetectCircleByTwoPointer(LeetCode142Node head)
{
if (head?.next == null)
{
return(null);
}
var slow = head;
var fast = head;
while (fast?.next != null)
{
fast = fast.next.next;
slow = slow.next;
if (fast == slow)
{
slow = head;
while (slow != fast)
{
slow = slow.next;
fast = fast.next;
}
return(slow);
}
}
return(null);
}
public static LeetCode142Node DetectCircleHashMap(LeetCode142Node head)
{
var hashMap = new HashSet <LeetCode142Node> ();
while (head != null)
{
if (!hashMap.Contains(head))
{
hashMap.Add(head);
head = head.next;
}
else
{
return(head);
}
}
return(null);
}
public LeetCode142Node(int x)
{
val = x;
next = null;
}