func main() {
    
    n1:=&LoopNode{}
    n2:=&LoopNode{}
    n3:=&LoopNode{}
    n4:=&LoopNode{}
    n5:=&LoopNode{}
    n1.next = n2
    n2.next = n3
    n3.next = n4
    n4.next = n5
    n5.next = n1
   flag := checkLoopNode(n1)
   println(flag)

}

type LoopNode struct{
    val int
    next *LoopNode
}

func checkLoopNode(head *LoopNode) bool{

    if head == nil {
        return false
    }

    fast := head.next
    slow := head

    for fast != nil {
        if slow == fast{
            return true
        }
        fast = fast.next
    }
    return false
    
}
输出：true