浙大数据结构第二版 习题3.5 求链表的倒数第m个元素 答案错了一点

ElementType Find( List L, int m )
{
    List p1 = L;
    List p2 = L;
    List pLast = NULL;
    int c = 0;
    while (p1) {
        if (c == m) {
            p2 = L;
        }
        p1 = p1->Next;
        p2 = p2->Next;
        pLast = p2;
        c++;
    }
    if (c > m)
        return pLast->Data;      else
        return -1;
}

ElementType Find( List L, int m )
{
    List pCurrent = L;
    List pFind = L;
    for (int i =0; i<m;i++)
        if (pCurrent)
            pCurrent = pCurrent->Next;
        else
            return -1;
    while (pCurrent) {
        pFind = pFind->Next;
        pCurrent = pCurrent->Next;
    }
    return pFind->Data;
}