单链表反转

List Reverse(List head)
{
    if (head == NULL || head->Next == NULL) {
        return head;
    }
    List p;
    List q;
    List r;
    p = head;
    q = head->Next;
    head->Next = NULL;
    while (q) {
        r = q->Next;
        q->Next = p;
        p = q;
        q = r;//最后的时候q=NULL
    }
    head = p;
    return head;
}