/// <summary>
/// CalculateUnion determines the roots involved and performs a union between
/// two squares values (representing two points in the maze).
/// On a success it returns a Pair object with the information necessary to later
/// pass on to observers (a GridPoint, and a direction). On a failure (which shouldn't
/// happen) it returns null.
/// </summary>
/// <param name="randomNumber">the GridPoint to exit from</param>
/// <param name="gridPoint">the new GridPoint the exit leads to</param>
/// <returns>an object of the Pair class, with Integer and GridPoint.Direction values,
/// or null on failure</returns>
private Pair <int, GridPoint.Direction> CalculateUnion(GridPoint gridPoint, GridPoint newPoint)
{
//Variables
int here = GetSquareId(gridPoint); //cell value of GridPoint
int next = GetSquareId(newPoint); //cell value of newPoint
int hereRoot = 0;
int nextRoot = 0;
//find the root of here
try {
hereRoot = disjointSet.Find(here);
}
catch (Exception e)
{
MessageBox.Show(e.Message);
}
//find the root of next
try {
nextRoot = disjointSet.Find(next);
}
catch (Exception e)
{
MessageBox.Show(e.Message);
}
//if a value of 0 is returned, it is a top root. Use its square
//value instead.
if (hereRoot == 0)
{
hereRoot = here;
}
else if (nextRoot == 0)
{
nextRoot = next;
}
//attempt union, and return a Pair object if successful
try {
disjointSet.Union(nextRoot, hereRoot);
//Adds edges to the extended graph
extendedGraph.AddEdge(here, next, 1);
extendedGraph.AddEdge(next, here, 1);
return(new Pair <int, GridPoint.Direction>(here, gridPoint.GetDirection(newPoint)));
}
catch (Exception e)
{
MessageBox.Show("Union error: " + here + " " + next + " ; " + e.Message);
}
return(null);
}