using System;
class Program
{
// A sparse matrix is a matrix in which the majority of elements are zero.
// To compact a sparse matrix, use a method to store only the non‑zero
// entries using a triplet representation (row, column, value).
// This reduces memory usage.
// Convert a sparse matrix into compact (triplet) form
static int[,] CompactMatrix(int[,] matrix)
{
int rows = matrix.GetLength(0);
int cols = matrix.GetLength(1);
// Count non-zero elements
int count = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
if (matrix[i, j] != 0) {
count++;
}
}
}
// Compact matrix has 3 rows: row index, col index, value
int[,] compact = new int[3, count];
int k = 0;
// Fill compact matrix
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
if (matrix[i, j] != 0) {
compact[0, k] = i; // row
compact[1, k] = j; // column
compact[2, k] = matrix[i, j]; // value
k++;
}
}
}
return compact;
}
static void Main()
{
int[,] matrix = {
{0, 0, 3, 0, 8, 0, 0, 0, 0},
{0, 0, 5, 7, 0, 0, 1, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 2, 6, 0, 0, 4, 0, 0, 0},
{0, 0, 0, 0, 9, 0, 0, 0, 0}
};
int[,] compact = CompactMatrix(matrix);
Console.WriteLine("Compact matrix:");
for (int i = 0; i < 3; i++) {
for (int j = 0; j < compact.GetLength(1); j++) {
Console.Write(compact[i, j] + " ");
}
Console.WriteLine();
}
}
}
/*
run:
Compact matrix:
0 0 1 1 1 3 3 3 4
2 4 2 3 6 1 2 5 4
3 8 5 7 1 2 6 4 9
*/
