public IEnumerable <Tile> GetPath(Tile start, Tile target)
{
if (start == target)
{
return(new[] { start });
}
var allTiles = Grid.Flatten().ToArray();
var distances = allTiles.ToDictionary(t => t, l => 100_000);
var bestPrev = allTiles.ToDictionary(t => t, l => (Tile)null);
var stillToVisit = new HashSet <Tile>(allTiles);
distances[start] = 0;
while (stillToVisit.Any())
{
var nodeWithShortestDistance =
distances.Where(l => stillToVisit.Contains(l.Key)).OrderBy(l => l.Value).First().Key;
var nodeDistance = distances[nodeWithShortestDistance];
stillToVisit.Remove(nodeWithShortestDistance);
var distCandidate = nodeDistance + 1;
foreach (var neighbor in nodeWithShortestDistance.GetNeighbors(Grid).Intersect(stillToVisit))
{
if (distances[neighbor] > distCandidate)
{
distances[neighbor] = distCandidate;
bestPrev[neighbor] = nodeWithShortestDistance;
}
}
}
var result = new List <Tile>();
//var targetReached = bestPrev.TryGetValue(target, out var _);
var targetReached = bestPrev.ContainsKey(target) && bestPrev[target] != null;
if (targetReached)
{
result = BacktrackFromTarget(target, bestPrev);
}
else
{
var reachableTiles = bestPrev.Where(l => l.Value != null);
if (!reachableTiles.Any())
{
result.Add(start);
}
else
{
var hitTilesNearestToTarget = reachableTiles.Select(l => l.Key)
.Concat(new[] { start })
.GroupBy(h => Distance(h, target))
.OrderBy(g => g.Key)
.First();
var nearTargetHitWithBestWayToStart =
hitTilesNearestToTarget.OrderBy(l => distances[l]).FirstOrDefault();
result = BacktrackFromTarget(nearTargetHitWithBestWayToStart, bestPrev);
}
}
result.Reverse();
return(result);
}
