51nod 1027大数乘法

直接模板了。
 1 #include<cstdio>
 2 #include<cstring>
 3 using namespace std;
 4 const int N = 1001;
 5 const int DLEN = 4;
 6 const int mod = 10000;
 7 int alen, blen;
 8 int ans_len;
 9 char a1[N], b1[N];
10 int a[600], b[600];
11 int ans[600];
12 
13 void BigInt(const char s[], int (&c)[600], int &len){
14     memset(c, 0, sizeof(c));
15     int L = strlen(s);
16     len = L / DLEN;
17     if(L%DLEN) len++;
18     int cnt = 0;
19     for(int i = L-1; i >= 0 ; i -= DLEN){
20         int k = i - DLEN + 1;
21         if(k < 0) k = 0;
22         int t = 0;
23         for(int j = k; j <= i; ++j)
24             t = t * 10 + s[j] - '0';
25         c[cnt++] = t;
26     }
27 }
28 void multi(){
29     int i, j;
30     for(i = 0; i < alen; ++i){
31         int up = 0;
32         for(j = 0; j < blen; ++j){
33             int t = a[i] * b[j] + ans[i+j] + up;
34             up = t / mod;
35             ans[i+j] = t % mod;
36         }
37         if(up != 0)
38             ans[i+j] = up;
39     }
40     ans_len = alen + blen;
41     while(ans[ans_len-1] == 0 && ans_len > 1)
42         ans_len--;
43 
44     printf("%d", ans[ans_len-1]);
45     for(i = ans_len-2; i >= 0; i--)
46         printf("%04d", ans[i]);
47     puts("");
48 }
49 int main(){
50     scanf("%s%s", a1, b1);
51     BigInt(a1, a, alen);
52     BigInt(b1, b, blen);
53     multi();
54     return 0;
55 }
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