142-linked-list-cycle-ii.go

package main

func detectCycle(head *ListNode) *ListNode {
	fast, slow := head, head
	for fast != nil && fast.Next != nil {
		fast = fast.Next.Next
		slow = slow.Next

		if fast == slow {
			fast = head
			for fast != slow {
				fast = fast.Next
				slow = slow.Next
			}
			return fast
		}
	}
	return nil
}