/// <summary>
/// Gets the best possible path (approximate solution) using a A* alogrithm.
/// </summary>
/// <param name="start"></param>
/// <param name="target"></param>
/// <param name="minSecurityLevel">The mininmum, inclusive, security level.</param>
/// <returns></returns>
private static PathFinder FindBestPathCore(SolarSystem start, SolarSystem target, float minSecurityLevel)
{
var bestDepthes = new Dictionary<SolarSystem, int>();
var paths = new SortedList<float, PathFinder>();
PathFinder root = new PathFinder(start);
bestDepthes.Add(start, -1);
paths.Add(0, root);
while (true)
{
if (paths.Count == 0) return null;
PathFinder best = null;
int depth = 0;
// Pick the best candidate path, but ensures it matches the best depth found so far
while (true)
{
// Picks the best one, returns if we found our target
best = paths.Values[0];
if (best.m_system == target) return best;
// Removes it from the list
paths.RemoveAt(0);
int bestDepth;
depth = best.Depth;
bestDepthes.TryGetValue(best.m_system, out bestDepth);
if (bestDepth == depth || best.m_system == start) break;
}
// Gets the subpaths for the best path so far.
depth++;
foreach (var child in best.GetChildren(depth, bestDepthes))
{
// Gets the heuristic key: the shorter, the better the candidate.
var key = child.m_system.GetSquareDistanceWith(target) * (float)(depth * depth);
if (child.m_system.SecurityLevel < minSecurityLevel) key *= 100.0f;
while (paths.ContainsKey(key)) key++;
// Stores it in the sorted list.
paths.Add(key, child);
}
}
}
/// <summary>
/// Constructor for a child.
/// </summary>
/// <param name="parent"></param>
/// <param name="system"></param>
private PathFinder(PathFinder parent, SolarSystem system)
{
m_parent = parent;
m_system = system;
}
/// <summary>
/// Constructor for a starting point
/// </summary>
/// <param name="system"></param>
private PathFinder(SolarSystem system)
{
m_parent = null;
m_system = system;
}
/// <summary>
/// Constructor for a child.
/// </summary>
/// <param name="parent"></param>
/// <param name="system"></param>
private PathFinder(PathFinder parent, SolarSystem system)
{
m_parent = parent;
m_system = system;
}
/// <summary>
/// Constructor for a starting point
/// </summary>
/// <param name="system"></param>
private PathFinder(SolarSystem system)
{
m_parent = null;
m_system = system;
}
/// <summary>
/// Find the guessed shortest path using a A* (heuristic) algorithm.
/// </summary>
/// <param name="target">The target system.</param>
/// <param name="minSecurityLevel">The mininmum, inclusive, real security level. Systems have levels between -1 and +1.</param>
/// <returns>The list of systems, beginning with this one and ending with the provided target.</returns>
public List <SolarSystem> GetFastestPathTo(SolarSystem target, float minSecurityLevel)
{
return(PathFinder.FindBestPath(this, target, minSecurityLevel));
}