代码

#define idx(i,j) i * n + j
#define fo(i,x,y) for(int i = x;i < y;++i)

void matrix_multiply(int n, const double *A, const double *B, double *C)
{
	fo(i,0,n * n) C[i] = 0;
	fo(i,0,n) fo(k,0,n) if(A[idx(i,k)]) fo(j,0,n) C[idx(i,j)] += A[idx(i,k)] * B[idx(k,j)];
}

评测结果