using System;
namespace DatabaseSchemaReader.Utilities
{
/// <summary>
/// Sorts a graph by the dependencies.
/// </summary>
/// <remarks>
/// Copied directly from http://tawani.blogspot.com/2009/02/topological-sorting-and-cyclic.html
/// (in turn from a Java example).
/// </remarks>
class TopologicalSorter
{
private readonly int[] _vertices; // list of vertices
private readonly int[,] _matrix; // adjacency matrix
private int _numVerts; // current number of vertices
private readonly int[] _sortedArray;
public TopologicalSorter(int size)
{
_vertices = new int[size];
_matrix = new int[size, size];
for (int i = 0; i < size; i++)
for (int j = 0; j < size; j++)
_matrix[i, j] = 0;
_sortedArray = new int[size]; // sorted vert labels
}
public int AddVertex(int vertex)
{
_vertices[_numVerts++] = vertex;
return _numVerts - 1;
}
public void AddEdge(int start, int end)
{
_matrix[start, end] = 1;
}
public int[] Sort() // toplogical sort
{
while (_numVerts > 0) // while vertices remain,
{
// get a vertex with no successors, or -1
int currentVertex = NoSuccessors();
if (currentVertex == -1) // must be a cycle
throw new InvalidOperationException("Graph has cycles");
// insert vertex label in sorted array (start at end)
_sortedArray[_numVerts - 1] = _vertices[currentVertex];
DeleteVertex(currentVertex); // delete vertex
}
// vertices all gone; return sortedArray
return _sortedArray;
}
// returns vert with no successors (or -1 if no such verts)
private int NoSuccessors()
{
for (int row = 0; row < _numVerts; row++)
{
bool isEdge = false; // edge from row to column in adjMat
for (int col = 0; col < _numVerts; col++)
{
if (_matrix[row, col] > 0) // if edge to another,
{
isEdge = true;
break; // this vertex has a successor try another
}
}
if (!isEdge) // if no edges, has no successors
return row;
}
return -1; // no
}
private void DeleteVertex(int delVert)
{
// if not last vertex, delete from vertexList
if (delVert != _numVerts - 1)
{
for (int j = delVert; j < _numVerts - 1; j++)
_vertices[j] = _vertices[j + 1];
for (int row = delVert; row < _numVerts - 1; row++)
MoveRowUp(row, _numVerts);
for (int col = delVert; col < _numVerts - 1; col++)
MoveColLeft(col, _numVerts - 1);
}
_numVerts--; // one less vertex
}
private void MoveRowUp(int row, int length)
{
for (int col = 0; col < length; col++)
_matrix[row, col] = _matrix[row + 1, col];
}
private void MoveColLeft(int col, int length)
{
for (int row = 0; row < length; row++)
_matrix[row, col] = _matrix[row, col + 1];
}
}
}
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