矩阵乘法模板

#include<bits/stdc++.h>
using namespace std;
int mod ;

struct Matrix {
        int n , m ;
        int mat[4][4] ;
        int * operator [] (int x) {
               return mat[x] ;
        }
} ;

Matrix operator * (Matrix &x , Matrix &y) {
       Matrix res ;
       res.n = x.n , res.m = y.m ;
       memset (res.mat , 0 , sizeof(res.mat) ) ;
       for (int i = 0 ; i < x.n ; i ++) {
               for (int j = 0 ; j < y.m ; j ++) {
                       for (int k = 0 ; k < x.m ; k ++) {
                               int tmp = (int) (1ll*x[i][k] * y[k][j] % mod ) ;
                               res[i][j] = (res[i][j] + tmp) % mod ;
                       }
               }
       }
       return res ;
}

int main () {
        Matrix x , y ;
        x = {2 , 2 , {{1 , 0} , {2, 3}} } ;
        y = {2 , 2 , {{2 , 1} , {3, 4}} } ;
        mod = 1000 ;
        Matrix z = x * y ; 
        for (int i = 0 ; i < 2 ; i ++) {
                for (int j = 0 ; j < 2 ; j++) {
                        cout << z[i][j] << " " ;
                } cout << endl ;
        }
        return 0 ;
}