CppCodes/matrix-mult.cpp at main · maramsumanth/CppCodes · GitHub

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

#define ROW_1 4
#define COL_1 4

#define ROW_2 4
#define COL_2 4

void print(string display, vector<vector<int> > matrix,
           int start_row, int start_column, int end_row,
           int end_column)
{
    cout << endl << display << " =>" << endl;
    for (int i = start_row; i <= end_row; i++) {
        for (int j = start_column; j <= end_column; j++) {
            cout << setw(10);
            cout << matrix[i][j];
        }
        cout << endl;
    }
    cout << endl;
    return;
}

void add_matrix(vector<vector<int> > matrix_A,
                vector<vector<int> > matrix_B,
                vector<vector<int> >& matrix_C,
                int split_index)
{
    for (auto i = 0; i < split_index; i++)
        for (auto j = 0; j < split_index; j++)
            matrix_C[i][j]
                = matrix_A[i][j] + matrix_B[i][j];
}

vector<vector<int> >
multiply_matrix(vector<vector<int> > matrix_A,
                vector<vector<int> > matrix_B)
{
    int col_1 = matrix_A[0].size();
    int row_1 = matrix_A.size();
    int col_2 = matrix_B[0].size();
    int row_2 = matrix_B.size();

    if (col_1 != row_2) {
        cout << "\nError: The number of columns in Matrix "
                "A  must be equal to the number of rows in "
                "Matrix B\n";
        return {};
    }

    vector<int> result_matrix_row(col_2, 0);
    vector<vector<int> > result_matrix(row_1,
                                       result_matrix_row);

    if (col_1 == 1)
        result_matrix[0][0]
            = matrix_A[0][0] * matrix_B[0][0];
    else {
        int split_index = col_1 / 2;

        vector<int> row_vector(split_index, 0);
        vector<vector<int> > result_matrix_00(split_index,
                                              row_vector);
        vector<vector<int> > result_matrix_01(split_index,
                                              row_vector);
        vector<vector<int> > result_matrix_10(split_index,
                                              row_vector);
        vector<vector<int> > result_matrix_11(split_index,
                                              row_vector);

        vector<vector<int> > a00(split_index, row_vector);
        vector<vector<int> > a01(split_index, row_vector);
        vector<vector<int> > a10(split_index, row_vector);
        vector<vector<int> > a11(split_index, row_vector);
        vector<vector<int> > b00(split_index, row_vector);
        vector<vector<int> > b01(split_index, row_vector);
        vector<vector<int> > b10(split_index, row_vector);
        vector<vector<int> > b11(split_index, row_vector);

        for (auto i = 0; i < split_index; i++)
            for (auto j = 0; j < split_index; j++) {
                a00[i][j] = matrix_A[i][j];
                a01[i][j] = matrix_A[i][j + split_index];
                a10[i][j] = matrix_A[split_index + i][j];
                a11[i][j] = matrix_A[i + split_index]
                                    [j + split_index];
                b00[i][j] = matrix_B[i][j];
                b01[i][j] = matrix_B[i][j + split_index];
                b10[i][j] = matrix_B[split_index + i][j];
                b11[i][j] = matrix_B[i + split_index]
                                    [j + split_index];
            }

        add_matrix(multiply_matrix(a00, b00),
                   multiply_matrix(a01, b10),
                   result_matrix_00, split_index);
        add_matrix(multiply_matrix(a00, b01),
                   multiply_matrix(a01, b11),
                   result_matrix_01, split_index);
        add_matrix(multiply_matrix(a10, b00),
                   multiply_matrix(a11, b10),
                   result_matrix_10, split_index);
        add_matrix(multiply_matrix(a10, b01),
                   multiply_matrix(a11, b11),
                   result_matrix_11, split_index);

        for (auto i = 0; i < split_index; i++)
            for (auto j = 0; j < split_index; j++) {
                result_matrix[i][j]
                    = result_matrix_00[i][j];
                result_matrix[i][j + split_index]
                    = result_matrix_01[i][j];
                result_matrix[split_index + i][j]
                    = result_matrix_10[i][j];
                result_matrix[i + split_index]
                             [j + split_index]
                    = result_matrix_11[i][j];
            }

        result_matrix_00.clear();
        result_matrix_01.clear();
        result_matrix_10.clear();
        result_matrix_11.clear();
        a00.clear();
        a01.clear();
        a10.clear();
        a11.clear();
        b00.clear();
        b01.clear();
        b10.clear();
        b11.clear();
    }
    return result_matrix;
}

int main()
{
    vector<vector<int> > matrix_A = { { 1, 1, 1, 1 },
                                      { 2, 2, 2, 2 },
                                      { 3, 3, 3, 3 },
                                      { 2, 2, 2, 2 } };

    print("Array A", matrix_A, 0, 0, ROW_1 - 1, COL_1 - 1);

    vector<vector<int> > matrix_B = { { 1, 1, 1, 1 },
                                      { 2, 2, 2, 2 },
                                      { 3, 3, 3, 3 },
                                      { 2, 2, 2, 2 } };

    print("Array B", matrix_B, 0, 0, ROW_2 - 1, COL_2 - 1);

    vector<vector<int> > result_matrix(
        multiply_matrix(matrix_A, matrix_B));

    print("Result Array", result_matrix, 0, 0, ROW_1 - 1,
          COL_2 - 1);
}