大数乘法模板

计算 a * b

时间复杂度为 O(n^2)

代码:

 1 #include <iostream>
 2 using namespace std;
 3 
 4 const int MAXN = 1e4;
 5 int a[MAXN], b[MAXN], sol[MAXN], lena, lenb;
 6 
 7 void solve(void){
 8     int cnt = 0, indx = MAXN - 1;
 9     for(int i = lenb - 1; i >= 0; i--){
10         int pos = indx--;
11         for(int j = lena - 1; j >= 0; j--){
12             int cc = b[i] * a[j] + cnt + sol[pos];
13             sol[pos--] = cc % 10;
14             cnt = cc / 10;
15         }
16         sol[pos] += cnt;
17         cnt = 0;
18     }
19 }
20 
21 int main(void){
22     string s1, s2;
23     cin >> s1 >> s2;
24     lena = s1.size();
25     lenb = s2.size();
26     for(int i = 0; i < lena; i++){
27         a[i] = s1[i] - '0';
28     }
29     for(int i = 0; i < lenb; i++){
30         b[i] = s2[i] - '0';
31     }
32     solve();
33     int i = 0;
34     while(sol[i] == 0) i++;
35     while(i < MAXN) cout << sol[i++];
36     cout << endl;
37     return 0;
38 }

 

posted @ 2017-08-15 21:22  geloutingyu  阅读(321)  评论(0)  编辑  收藏  举报