Imports System
Module SparseMatrixModule
' 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
Function CompactMatrix(matrix As Integer(,)) As Integer(,)
Dim rows As Integer = matrix.GetLength(0)
Dim cols As Integer = matrix.GetLength(1)
' Count non-zero elements
Dim count As Integer = 0
For i As Integer = 0 To rows - 1
For j As Integer = 0 To cols - 1
If matrix(i, j) <> 0 Then
count += 1
End If
Next
Next
' Compact matrix has 3 rows: row index, col index, value
Dim compact(2, count - 1) As Integer
Dim k As Integer = 0
' Fill compact matrix
For i As Integer = 0 To rows - 1
For j As Integer = 0 To cols - 1
If matrix(i, j) <> 0 Then
compact(0, k) = i ' row
compact(1, k) = j ' column
compact(2, k) = matrix(i, j) ' value
k += 1
End If
Next
Next
Return compact
End Function
Sub Main()
Dim matrix As Integer(,) = {
{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}
}
Dim compact = CompactMatrix(matrix)
Console.WriteLine("Compact matrix:")
For i As Integer = 0 To 2
For j As Integer = 0 To compact.GetLength(1) - 1
Console.Write(compact(i, j) & " ")
Next
Console.WriteLine()
Next
Console.WriteLine()
Console.WriteLine("Press any key to exit...")
Console.ReadKey()
End Sub
End Module
' 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
'
