NC4 判断链表中是否有环

https://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9

这题还是挺简单的，判断环使用快慢指针就行了

func hasCycle( head *ListNode ) bool {
    if head == nil || head.Next == nil {return false}
    slow, fast := head, head.Next
    for fast != nil && fast.Next != nil {
        if fast.Val == slow.Val {
            return true
        }

        slow = slow.Next
        fast = fast.Next.Next
    }
    
    return false
}