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;
}