6-5 鏈式表操作集 (20 分)

題目地址：https://pintia.cn/problem-sets/15/problems/728

本題按照題目要求仔細模擬即可，需要注意的就是要插入到頭節點之前以及刪除頭節點的情況特判處理

List Insert(List L, ElementType X, Position P) {
    if(P == L) {
        List q = (List)malloc(sizeof(List));
        q->Data = X;
        q->Next = L;
        return q;
    }

    List q = L;
    while(q) {
        if(q->Next == P) {
            List p = (List)malloc(sizeof(List));
            p->Next = q->Next;
            p->Data = X;
            q->Next = p;
            return L;
        }
        q = q->Next;
    }
    printf("Wrong Position for Insertion\n");
    return ERROR;
}

List Delete(List L, Position P) {
    if(L == P) {
        return L->Next;
    }

    List q = L;
    while(q) {
        if(q->Next == P) {
            q->Next = q->Next->Next;
            return L;
        }
        q = q->Next;
    }
    printf("Wrong Position for Deletion\n");
    return ERROR;
}

Position Find(List L, ElementType X) {
    List q;
    q = L;
    while(q != NULL) {
        if(q->Data == X) {
            return q;
        }
        q = q->Next;
    }
    return ERROR;
}