// http://www.redblobgames.com/pathfinding/tower-defense/
private Dictionary <NodeType, T> BFS <T>(
NodeType start,
T initialValue,
StoppingPredicate stoppingPredicate,
GraphNeighbors graphNeighbors,
NeighborHandler <T> neighborHandler)
{
Queue <NodeType> frontier = new Queue <NodeType> ();
var accumulator = new Dictionary <NodeType, T> ();
frontier.Enqueue(start);
accumulator[start] = initialValue;
while (frontier.Count > 0)
{
var current = frontier.Dequeue();
if (stoppingPredicate(current))
{
break;
}
foreach (var neighbor in graphNeighbors(current))
{
if (!accumulator.ContainsKey(neighbor))
{
frontier.Enqueue(neighbor);
neighborHandler(current, neighbor, accumulator);
}
}
}
return(accumulator);
}
/**
* Find the best path from `start` to get as close as possible to `dest`, within a limited number of steps
*/
public IEnumerable <NodeType> BestPathTowards(NodeType start, NodeType pos, GraphNeighbors graphNeighbors, int maxSteps)
{
var path = Path(start, pos, graphNeighbors);
UnityEngine.Debug.LogFormat("best path from {0} toward {1}: [{2}] {3}",
start,
pos,
string.Join(", ", Array.ConvertAll(path.ToArray(), i => i.ToString())),
path.Count());
return(path.Take(maxSteps));
}
public Dictionary <NodeType, int> DistancesToNode(NodeType node, GraphNeighbors graph)
{
// FIXME: cache this every turn
return(BFS <int>(
node,
0,
_ => false,
graph,
(current, neighbor, acc) => {
acc[neighbor] = 1 + acc[current];
}));
}
public IEnumerable <NodeType> Path(NodeType start, NodeType pos, GraphNeighbors graphNeighbors)
{
var comeFrom = BFS <NodeType> (
start,
start,
current => current.Equals(pos),
graphNeighbors,
(current, neighbor, acc) => {
acc[neighbor] = current;
});
var path = new List <NodeType> ();
// foreach (var pair in comeFrom) {
//// UnityEngine.Debug.LogFormat("{0} = {1}", pair.Key, pair.Value);
// }
// backtrack the dictionary to build the path
var c = pos;
path.Add(c);
while (true)
{
NodeType parent;
var ok = comeFrom.TryGetValue(c, out parent);
if (!ok || parent.Equals(start))
{
break;
}
else
{
path.Insert(0, parent);
c = parent;
}
}
return(path);
}
