void GaussPartialSparseMatrix(int n, vector<double> x, vector< vector<double> > a, vector<double> b){
    printf("\n%-35s", "GAUSS PARTIAL FOR SPARSE MATRIX");
    for(int p = 0; p < n; p++){
        // find pivot row and swap
        int max = p; // indeks najwiekszego
        for(int i = p+1; i < n; i++){
            if(abs(a[i][p]) > abs(a[max][p]))
                max = i;
        }

        a[p].swap(a[max]);
        swap(b[p], b[max]);


        // pivot within A and B
        for(int i = p+1; i < n; i++){
            // i wiersz
            // sprawdzenie czy element zerowy jesli tak przejscie do nastepnego wiersza
            if (a[i][p] == 0) continue;

            double alpha = a[i][p]/a[p][p];
            b[i] = b[i] - (alpha * b[p]);


            for(int j = p; j < n; j++){
                a[i][j] = a[i][j] - (alpha * a[p][j]);
            }
        }
    }

    for(int i = n - 1; i >= 0; i--){
        double sum = 0;
        for(int j = i+1; j < n; j++){
            sum += a[i][j] * x[j];
        }
        x[i] = (b[i] - sum)/a[i][i];
    }

    WYNIK = x[0];
    // cout<<"\nThe Solution is : \n";
    // for(int i=0;i<n;i++) {
    //     cout<<"\nx("<<i<<") = "<<x[i]<<"\n";
    // }

    cout << ": x[0] = " << WYNIK;

    // cout << "====================\n";
    //getch();
}