go语言学习---判断链表是否有环

package main
import "fmt"

type ListNode struct{
    val int
    next *ListNode
}

func hasCycle(head *ListNode) bool{
    if head == nil || head.next == nil{
        return false
    }

    var slow, fast = head, head.next
    for fast != slow{
        if fast == nil || fast.next == nil{
            return false
        }
        slow = slow.next
        fast = fast.next.next
    }
    return true
}

func main(){
    a := new(ListNode)
    a.val = 1

    b := new(ListNode)
    b.val = 2

    c := new(ListNode)
    c.val = 3

    a.next = b
    b.next = c

    fmt.Println(hasCycle(a))
}