/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
func hasCycle(head *ListNode) bool {
valMap:=map[*ListNode]bool{}
for head!=nil{
if _,ok:=valMap[head];ok{
return true
}else{
valMap[head]=true
head=head.Next
}
}
return false
}