protected override int Part2(string[] input)
{
var maze = new PortalMaze(input);
var shortestPath = MaxDepths().Select(d => FindMinimumDistanceBfsPlutonian(maze, d)).First(x => x != Infinite);
return(shortestPath);
}
protected override int Part1(string[] input)
{
var maze = new PortalMaze(input);
var graph = PortalGraph.BuildWeightedGraphFromMaze(maze);
var shortestPath = graph.ShortestPathDijkstra(maze.Entry, maze.Exit);
return(shortestPath);
}
private static int FindMinimumDistanceBfsPlutonian(PortalMaze maze, int maxDepth)
{
var graph = BuildSimpleGraph(maze);
var toplevel = new MazeLevel()
{
Level = 0
};
var entry = graph.Vertices[maze.Entry];
var exit = graph.Vertices[maze.Exit];
var root = graph.Root;
toplevel.Visited[root.Pos] = true;
var queue = new Queue <(MazeLevel, PortalGraph.Vertex, int)>();
queue.Enqueue((toplevel, root, 0));
while (queue.Any())
{
var(level, node, distance) = queue.Dequeue();
if (node.Pos == exit.Pos && level.Level == 0)
{
return(distance);
}
foreach (var e in node.Edges)
{
var nextnode = e.Key;
var nextlevel = level;
if (e.Value != 0)
{
if (e.Value == -1)
{
if (level.Level > maxDepth)
{
continue;
}
if (level.Inner == null)
{
level.Inner = new MazeLevel()
{
Level = level.Level + 1,
Outer = level
};
}
nextlevel = level.Inner;
}
else
{
nextlevel = level.Outer;
if (nextlevel == null)
{
continue;
}
}
nextnode = graph.Vertices[nextnode.Pos];
}
if (nextlevel.Visited[nextnode.Pos])
{
continue;
}
nextlevel.Visited[nextnode.Pos] = true;
queue.Enqueue((nextlevel, nextnode, distance + 1));
}
}
return(Infinite);
}
private static PortalGraph BuildSimpleGraph(PortalMaze maze)
{
var walked = new SparseMap <PortalGraph.Vertex>();
var graph = new PortalGraph();
graph.AddVertex(maze.Entry);
BuildSimpleGraph(graph.Root);
return(graph);
void BuildSimpleGraph(PortalGraph.Vertex node)
{
while (walked[node.Pos] == null)
{
walked[node.Pos] = node;
var positions = node.Pos
.LookAround()
.Select(p => new { Pos = p, Dest = maze.Transform(p) })
.Where(x => maze.Map[x.Dest] == '.')
.Where(x => walked[x.Dest] == null || !walked[x.Dest].Edges.ContainsKey(node))
.ToList();
foreach (var p in positions.Where(x => walked[x.Dest] != null).ToList())
{
var existing = walked[p.Dest];
var portal = maze.Portals[p.Pos];
var portalValue = portal == null ? 0 : portal.IsDownward ? -1 : 1;
var portalName = portal == null ? null : portal.Name;
node.Value = portal;
existing.Value = portal;
node.Edges[existing] = portalValue;
existing.Edges[node] = -portalValue;
positions.Remove(p);
}
switch (positions.Count())
{
case 0:
return;
case 1:
var p = positions.First();
var next = graph.AddVertex(p.Dest);
//graph.Vertices.Add(next);
var portal = maze.Portals[p.Pos];
var portalValue = portal == null ? 0 : portal.IsDownward ? -1 : 1;
node.Value = portal;
next.Value = portal;
node.Edges[next] = portalValue;
next.Edges[node] = -portalValue;
node = next;
break;
default:
var forks = positions.Select(x => graph.AddVertex(x.Dest)).ToList();
foreach (var fork in forks)
{
BuildSimpleGraph(fork);
}
return;
}
}
}
}
