141. 环形链表

快慢指针

func hasCycle(head *ListNode) bool {
    if head==nil||head.Next==nil {
        return false
    }
    for head!=nil{
        if head.Val==1>>63 {
            return true
        }
        head.Val = 1>>63
        head = head.Next
    }
    return false
}

map

func hasCycle2(head *ListNode) bool {
    if head==nil||head.Next==nil {
        return false
    }
    m :=make(map[uintptr]struct{})
    for head!=nil{
        if _,ok:=m[uintptr(unsafe.Pointer(head))];ok {
            return true
        }
        m[uintptr(unsafe.Pointer(head))] = struct{}{}
        head = head.Next
    }
    return false
}