hdu--4920--原来一直写了速度慢的矩阵乘法

 1 #include <iostream>
 2 #include <cstring>
 3 using namespace std;
 4 
 5 const int size = 810;
 6 int x[size][size];
 7 int y[size][size];
 8 int z[size][size];
 9 
10 int main()
11 {
12     cin.sync_with_stdio(false);
13     int n , num;
14     while( cin >> n )
15     {
16         memset( z , 0 , sizeof(z) );
17         for( int i = 0 ; i<n ; i++ )
18         {
19             for( int j = 0 ; j<n ; j++ )
20             {
21                 cin >> num;
22                 x[i][j] = num % 3;
23             }
24         }
25         for( int i = 0 ; i<n ; i++ )
26         {
27             for( int j = 0 ; j<n ; j++ )
28             {
29                 cin >> num;
30                 y[i][j] = num % 3;
31             }
32         }
33         for( int i = 0 ; i<n ; i++ )
34         {
35             for( int k = 0 ; k<n ; k++ )
36             {
37                 if( x[i][k] )
38                 {
39                     for( int j = 0 ; j<n ; j++ )
40                     {
41                         z[i][j] += x[i][k] * y[k][j];
42                     }
43                 }
44             }
45         }
46         for( int i = 0 ; i<n ; i++ )
47         {
48             cout << (z[i][0]%3);
49             for( int j = 1 ; j<n ; j++ )
50             {
51                 cout << " " << (z[i][j]%3) ;
52             }
53             cout << endl;
54         }
55     }
56     return 0;
57 }