/*
C code of two 2 by 2 matrix multiplication using Strassen's algorithm
*/
#include<stdio.h>
int main()
{
    int a[2][2], b[2][2], c[2][2], i, j;
    int m1, m2, m3, m4, m5, m6, m7;
    printf("Enter the 4 elements of first matrix: ");
    for(i = 0; i < 2; i++)
        for(j = 0; j < 2; j++)
            scanf("%d", &a[i][j]);
    printf("Enter the 4 elements of second matrix: ");
    for(i = 0; i < 2; i++)
        for(j = 0; j < 2; j++)
            scanf("%d", &b[i][j]);
    printf("\nThe first matrix is\n");
    for(i = 0; i < 2; i++)
        {
            printf("\n");
            for(j = 0; j < 2; j++)
                printf("%d\t", a[i][j]);
        }
    printf("\nThe second matrix is\n");
    for(i = 0; i < 2; i++)
        {
            printf("\n");
            for(j = 0; j < 2; j++)
                printf("%d\t", b[i][j]);
        }
    m1= (a[0][0] + a[1][1]) * (b[0][0] + b[1][1]);
    m2= (a[1][0] + a[1][1]) * b[0][0];
    m3= a[0][0] * (b[0][1] - b[1][1]);
    m4= a[1][1] * (b[1][0] - b[0][0]);
    m5= (a[0][0] + a[0][1]) * b[1][1];
    m6= (a[1][0] - a[0][0]) * (b[0][0]+b[0][1]);
    m7= (a[0][1] - a[1][1]) * (b[1][0]+b[1][1]);
    c[0][0] = m1 + m4- m5 + m7;
    c[0][1] = m3 + m5;
    c[1][0] = m2 + m4;
    c[1][1] = m1 - m2 + m3 + m6;
    printf("\nAfter multiplication using Strassen's algorithm \n");
    for(i = 0; i < 2 ; i++)
        {
            printf("\n");
            for(j = 0; j < 2; j++)
                printf("%d\t", c[i][j]);
        }
    return 0;
}

/*
Enter the 4 elements of first matrix:
1 2
3 4
Enter the 4 elements of second matrix:
5 6
7 8
The first matrix is

1 2
3 4
The second matrix is

5 6
7 8
After multiplication using Strassen's algorithm

19  22
43  50