习题3.3---只通过调整指针来达到相邻结点交换的过程

//单链表
void
ExchangeNear( List L, Position PosBefoP )
{
    Position PosL,PosR;
    PosL = PosBefoP->Next;
    PosR = PosL->Next;

    PosL->Next = PosR->Next;
    PosR->Next = PosL;
    PosBefoP->Next = PosR;
}
//双链表
void
ExchangeNear( Position PosBefoP, List L )
{
    Position P,PosAfteP;
    P = PosBefoP->Next;
    PosAfteP = P->Next;

    P->Next = PosAfteP->Next;
    P->front = PosAfteP;

    PosAfteP->Next = P;
    PosAfteP->front = PosBefoP;

    PosBefoP->Next = PosAfteP;
}