sparse matrix

[victorio]

How I can to write a sparse matrix

#include <iostream>
#include <vector>
#include <cstdlib>

using namespace std;
struct MatrizEncadeadaElemento {
	unsigned int linha, coluna;
	int valor;
};

class MatrizEncadeada {
	vector<MatrizEncadeadaElemento> dados;
public:
	void inserirMatriz(int** M, int qLinhas, int qColunas) {
		for (int i = 0; i < qLinhas; ++i) {
			for (int j = 0; j < qColunas; ++j) {
				if (M[i][j]) {
					MatrizEncadeadaElemento n(i, j, M[i][j]);
					dados.push_back(n);
				}
			}
		}
	}

	int lerPosicao(int linha, int coluna) {
		return 0;
	}

	vector<MatrizEncadeadaElemento> retornaLista() {
		return dados;
	}
};

int main() {
	MatrizEncadeada me;
	int m, n;
	int** matriz;
#ifdef __MINGW32__
	cout
			<< "Digite as dimensões da matriz (linhas e colunas) separadas por espaço "
			<< endl;
#endif
	cin >> m >> n;
	matriz = (int**) calloc(m, sizeof(int*));
	for (int i = 0; i < m; ++i)
		matriz[i] = (int*) calloc(n, sizeof(int));
	for (int i = 0; i < m; ++i) {
		for (int j = 0; j < n; ++j) {
#ifdef __MINGW32__
			cout << "Digite o elemento da posicao " << i << ' ' << j << endl;
#endif
			cin >> matriz[i][j];
		}
	}
	me.inserirMatriz(matriz, m, n);
	vector<MatrizEncadeadaElemento> v = me.retornaLista();
	for (unsigned int i = 0; i < v.size(); ++i)
		cout << v[i].linha << ' ' << v[i].coluna << ' ' << v[i].valor << endl;
	return 0;
}

[George P]

If you are going to use a std::vector do NOT use C memory management. A 2D vector (matrix) will handle its own memory usage.

Do NOT use C memory management in a C++ program. Use new if you must.

[George P]

std::vector is a possible choice to work with as a matrix:

#include <iostream>
#include <vector>

int main()
{
   std::cout << "What's the matrix outer size? ";
   int outer { };
   std::cin >> outer;

   std::cout << "What's the matrix inner size? ";
   int inner { };
   std::cin >> inner;
   std::cout << '\n';

   // create the sparsest matrix (2D vector) possible, ALL elements are zero
   std::vector<std::vector<int>> matrix(outer, std::vector<int>(inner));

   for (size_t outer_loop { }; outer_loop < outer; outer_loop++)
   {
      for (size_t inner_loop { }; inner_loop < inner; inner_loop++)
      {
         std::cout << matrix[outer_loop][inner_loop] << ' ';
      }
      std::cout << '\n';
   }
   std::cout << '\n';

   // create a faux matrix in 1D, still very sparse
   std::vector<int> faux_matrix(outer * inner);

   for (size_t outer_loop { }; outer_loop < outer; outer_loop++)
   {
      for (size_t inner_loop { }; inner_loop < inner; inner_loop++)
      {
         std::cout << faux_matrix[(outer_loop * outer) + inner_loop] << ' ';
      }
      std::cout << '\n';
   }
}

[George P]

If you absolutely need the matrix to be an array the best way is create the array as faux 2D.

#include <iostream>
#include <vector>

int main()
{
   std::cout << "What's the matrix outer size? ";
   int outer { };
   std::cin >> outer;

   std::cout << "What's the matrix inner size? ";
   int inner { };
   std::cin >> inner;
   std::cout << '\n';

   // create a faux matrix with a 1D array
   int* faux_matrix = new int[outer * inner]();

   for (size_t outer_loop { }; outer_loop < outer; outer_loop++)
   {
      for (size_t inner_loop { }; inner_loop < inner; inner_loop++)
      {
         std::cout << faux_matrix[(outer_loop * outer) + inner_loop] << ' ';
      }
      std::cout << '\n';
   }

   delete[] faux_matrix;
}

https://stackoverflow.com/questions/936687/how-do-i-declare-a-2d-array-in-c-using-new/16239446#16239446

[victorio]

I just have problem in this function, line 5 and 6. Why I can't create an object of class?

void inserirMatriz(int** M, int qLinhas, int qColunas) {
		for (int i = 0; i < qLinhas; ++i) {
			for (int j = 0; j < qColunas; ++j) {
				if (M[i][j]) {
					MatrizEncadeada n(i, j, M[i][j]);
					dados.push_back(n);
				}
			}
		}
	}

[lastchance]

https://eigen.tuxfamily.org/dox/group__SparseQuickRefPage.html