public WeightedDistances BFSMeetInMiddlePathTo(WeightedMazeCell goal)
{
Queue <WeightedMazeCell> grayQueue = new Queue <WeightedMazeCell>();
Queue <WeightedMazeCell> grayQueueGoal = new Queue <WeightedMazeCell>();
grayQueue.Enqueue(this.startingCell);
grayQueueGoal.Enqueue(goal);
WeightedDistances distances = new WeightedDistances(startingCell);
WeightedDistances distancesGoal = new WeightedDistances(goal);
bool notFound = true;
var current = startingCell;
while (notFound)
{
current = grayQueue.Dequeue();
foreach (var linkedCell in current.Links())
{
if (distancesGoal.ContainsKey(linkedCell))
{
notFound = false;
if (!distances.ContainsKey(linkedCell))
{
distances.Add(linkedCell, distances[current] + 1);
}
current = linkedCell;
break;
}
if (distances.ContainsKey(linkedCell))
{
continue;
}
distances.Add(linkedCell, distances[current] + 1);
if (grayQueue.Contains(linkedCell))
{
continue;
}
grayQueue.Enqueue(linkedCell);
}
if (!notFound)
{
break;
}
current = grayQueueGoal.Dequeue();
foreach (var linkedCell in current.Links())
{
if (distances.ContainsKey(linkedCell))
{
notFound = false;
if (!distancesGoal.ContainsKey(linkedCell))
{
distancesGoal.Add(linkedCell, distancesGoal[current] + 1);
}
current = linkedCell;
break;
}
if (distancesGoal.ContainsKey(linkedCell))
{
continue;
}
distancesGoal.Add(linkedCell, distancesGoal[current] + 1);
if (grayQueueGoal.Contains(linkedCell))
{
continue;
}
grayQueueGoal.Enqueue(linkedCell);
}
}
WeightedDistances breadcrumbs = new WeightedDistances(this.startingCell);
breadcrumbs.Add(current, distances[current]);
WeightedMazeCell breadcrumbsCurrent = current;
while (current != startingCell)
{
foreach (WeightedMazeCell neighbour in current.Links())
{
if (!distances.ContainsKey(neighbour))
{
continue;
}
if (distances[neighbour] < distances[current])
{
if (!breadcrumbs.ContainsKey(neighbour))
{
breadcrumbs.Add(neighbour, distances[neighbour]);
}
else
{
breadcrumbs[neighbour] = distances[neighbour];
}
current = neighbour;
break;
}
}
}
current = breadcrumbsCurrent;
WeightedDistances breadcrumbsGoal = new WeightedDistances(goal);
while (current != goal)
{
foreach (WeightedMazeCell neighbour in current.Links())
{
if (!distancesGoal.ContainsKey(neighbour))
{
continue;
}
if (distancesGoal[neighbour] < distancesGoal[current])
{
if (!breadcrumbsGoal.ContainsKey(neighbour))
{
breadcrumbsGoal.Add(neighbour, distancesGoal[neighbour]);
}
else
{
breadcrumbsGoal[neighbour] = distancesGoal[neighbour];
}
current = neighbour;
break;
}
}
}
WeightedMazeCell maxCell = null;
WeightedMazeCell minCell = null;
int max = breadcrumbsGoal.MaxDistanceValue();
int min = breadcrumbsGoal.MinDistanceValue();
while (max > min)
{
foreach (WeightedMazeCell cell in breadcrumbsGoal.Keys)
{
if (breadcrumbsGoal[cell] == min)
{
minCell = cell;
}
if (breadcrumbsGoal[cell] == max)
{
maxCell = cell;
}
}
breadcrumbsGoal[minCell] = max;
breadcrumbsGoal[maxCell] = min;
max--;
min++;
}
max = breadcrumbs.MaxDistanceValue();
max++;
foreach (WeightedMazeCell cell in breadcrumbsGoal.Keys)
{
breadcrumbs.Add(cell, breadcrumbsGoal[cell] + max);
}
return(breadcrumbs);
}
