大数相乘

class NodeData
{
public:
NodeData* next;
char num;
NodeData() {num = '0'; next = NULL;}
};

NodeData* SetUpLinkList()
{
NodeData* head = new NodeData;
bool is_add = true;
char data = 0;
NodeData* p = head;
while(1) {
cin >> data;
if ('a' == data ) break;
NodeData* cur = new NodeData;
cur->num = data;
cur->next = NULL;
p->next = cur;
p = cur;
}

NodeData* tmp = head;
head = head->next;
delete tmp;

return head;
}

NodeData* ReverseLink(NodeData*a)
{
NodeData* res = NULL;
if (NULL == a) return NULL;

NodeData* head = a;
NodeData* p = a;
NodeData* q = a->next;

while (NULL != q) {
NodeData* r = q->next;
q->next = p;
p = q;
q = r;
}

head->next = NULL;
res = p;

return res;
}

int digital_atoi(char chr)
{
return chr - '0';
}

char digital_itoa(int i)
{
return i + '0';
}

NodeData* Multiply(NodeData* a, NodeData* b)
{
NodeData* total = NULL;
if (NULL == a ||
NULL == b) return NULL;

NodeData* fir = ReverseLink(a);
NodeData* sec = ReverseLink(b);
int count = 0;
while (NULL != sec) {
int m = digital_atoi(sec->num);
int flow = 0;//进位
NodeData* head = new NodeData;
NodeData* p = head;
NodeData* left = fir;

while (NULL != left) {
int n = digital_atoi(left->num);
int subtotal = m * n;

int y = (subtotal + flow) % 10;
flow = (subtotal + flow) / 10;

NodeData* node = new NodeData;
node->num = digital_itoa(y);
p->next = node;
p = node;

left = left->next;
}

if (0 != flow) {
NodeData* node = new NodeData;
node->num = digital_itoa(flow);
p->next = node;
p = node;
}

//根据乘法竖式，得到某一位与被乘数相乘的结果，并且将此结果的低位用0补齐
NodeData* subtotal_head = new NodeData;
p = subtotal_head;
for (int i = 0; i < count; i++)
{
NodeData* node = new NodeData;
node->num = '0';
node->next = NULL;
p->next = node;
p = node;
}
p->next = head->next;
delete head;
NodeData* del_node = subtotal_head;
subtotal_head = subtotal_head->next;
delete del_node;

//算完了某一位的乘法后，将其结果与当前的total相加
NodeData* sum_head = new NodeData;
sum_head->next = NULL;
NodeData* tmp = sum_head;
flow = 0;
bool bflag_added = false;
while (NULL != total &&
NULL != subtotal_head) {
bflag_added = true;
int n = digital_atoi(total->num);
int m = digital_atoi(subtotal_head->num);
int sum = m + n;
int y = (sum + flow) % 10;
flow = (sum + flow) / 10;

NodeData* node = new NodeData;
node->num = digital_itoa(y);
node->next = NULL;
tmp->next = node;
tmp = node;

total = total->next;
subtotal_head = subtotal_head->next;
}

if (NULL != sum_head->next) {
del_node = sum_head;
sum_head = sum_head->next;
delete del_node;
}

//上面加完后，可能有进位，有可能部分没加完
if (bflag_added) {
NodeData* continue_node = NULL;
if (NULL != subtotal_head) {
continue_node = subtotal_head;
} else if (NULL != total) {
continue_node = total;
} else {
//Do nothing
}

while (NULL != continue_node)
{
int n = digital_atoi(continue_node->num);
int sum = n + flow;
int y = sum % 10;
flow = sum / 10;
NodeData* node = new NodeData;
node->num = digital_itoa(y);
tmp->next = node;
tmp = node;

continue_node = continue_node->next;
}

if (0 != flow) {
NodeData* node = new NodeData;
node->num = digital_itoa(flow);
node->next = NULL;
tmp->next = node;
}

//删除临时结点
while (NULL != subtotal_head) {
del_node = subtotal_head;
subtotal_head = subtotal_head->next;
delete del_node;
}

while (NULL != total) {
del_node = total;
total = total->next;
delete del_node;
}
} else {
sum_head = subtotal_head;
}

total = sum_head;
count++;

sec = sec->next;
}

total = ReverseLink(total);

return total;
}

int _tmain(int argc, _TCHAR* argv[])
{
NodeData*left = SetUpLinkList();
NodeData*right = SetUpLinkList();

NodeData* res = Multiply(left, right);
while (NULL != res) {
cout << res->num;
res = res->next;
}

while (NULL != res) {
NodeData* del_node = res;
res = res->next;
delete del_node;
}

}