List <SidetrackEdge> GetPaths(ViterbiNode eos, int maxCount, int costSlack)
{
var result = new List <SidetrackEdge>();
result.Add(null);
PathCosts.Add(BaseCost);
var sidetrackHeap = new PriorityQueue <SidetrackEdge>();
var sideTrackEdge = Sidetracks[eos];
while (sideTrackEdge != null)
{
sidetrackHeap.Add(sideTrackEdge);
sideTrackEdge = sideTrackEdge.NextOption;
}
for (var i = 1; i < maxCount; i++)
{
if (sidetrackHeap.Count == 0)
{
break;
}
sideTrackEdge = sidetrackHeap.Dequeue();
if (sideTrackEdge.Cost > costSlack)
{
break;
}
result.Add(sideTrackEdge);
PathCosts.Add(BaseCost + sideTrackEdge.Cost);
var nextSidetrack = Sidetracks[sideTrackEdge.Tail];
while (nextSidetrack != null)
{
var next = new SidetrackEdge(nextSidetrack.Cost, nextSidetrack.Tail, nextSidetrack.Head);
next.Parent = sideTrackEdge;
sidetrackHeap.Add(next);
nextSidetrack = nextSidetrack.NextOption;
}
}
return(result);
}
/// <summary>
/// Get up to maxCount shortest paths with cost at most OPT + costSlack, where OPT is the optimal solution. The results are ordered in ascending order by cost.
/// </summary>
/// <param name="lattice">an instance of ViterbiLattice prosecced by a ViterbiSearcher</param>
/// <param name="maxCount">the maximum number of results</param>
/// <param name="costSlack">the maximum cost slack of a path</param>
/// <returns>the shortest paths and their costs</returns>
public MultiSearchResult GetShortestPaths(ViterbiLattice lattice, int maxCount, int costSlack)
{
PathCosts.Clear();
Sidetracks.Clear();
var multiSearchResult = new MultiSearchResult();
BuildSidetracks(lattice);
var eos = lattice.EndIndexArr[0][0];
BaseCost = eos.PathCost;
var paths = GetPaths(eos, maxCount, costSlack);
foreach (var(path, cost) in paths.Zip(Enumerable.Range(0, paths.Count), (p, i) => Tuple.Create(p, PathCosts[i])))
{
var nodes = GeneratePath(eos, path);
multiSearchResult.Add(nodes, cost);
}
return(multiSearchResult);
}
