Added a solver method for handling the last unsolved clue in a line.

Author: MeltyPlayer

FinModelUtility/Fin/Fin.Picross/src/PicrossSolver.cs

@@ -16,13 +16,15 @@ public IReadOnlyList<IReadOnlySet<IPicrossMove>> Solve(
     var columnClueStates = ToClueStates_(clues.Columns);
     var columnLineStates = columnClueStates
                            .Select((clues, x) => new PicrossLineState {
+                               IsColumn = true,
                                ClueStates = clues,
                                CellStates = boardState.GetColumn(x).ToArray(),
                            })
                            .ToArray();
     var rowClueStates = ToClueStates_(clues.Rows);
     var rowLineStates = rowClueStates
                         .Select((clues, y) => new PicrossLineState {
+                            IsColumn = false,
                             ClueStates = clues,
                             CellStates = boardState.GetRow(y).ToArray(),
                         })
@@ -122,13 +124,15 @@ private static readonly IReadOnlyList<IPicrossSolverMethod> SOLVER_METHODS_
       = [
           new AlreadySolvedPicrossSolverMethod(),
           new ExtendFirstClueSolverMethod(),
+          // TODO: Get rid of this
           new ExtendLastClueSolverMethod(),
           new FillSmallestUnknownsBetweenEmptiesSolverMethod(),
           new GapsAroundFirstClueSolverMethod(),
           new GapsAroundKnownCluesSolverMethod(),
           new GapsBetweenKnownCluesSolverMethod(),
           new GapsBetweenNeighboringCluesSolverMethod(),
           new GapsBetweenNeighboringShortCluesSolverMethod(),
+          new LastClueSolverMethod(),
           new MatchingBiggestOrUniqueLengthSolverMethod(),
       ];
 
@@ -385,7 +389,7 @@ var targetI
       if (isFirstClue && clueUnknownCount == 0 && !clueState.Solved) {
         var clueStartI = forward ? i : i + increment * (clueLength - 1);
         yield return new PicrossClueMove(
-            PicrossClueMoveSource.FIRST_CLUE,
+            PicrossClueMoveSource.FIRST_CLUE_IN_LINE,
             clueState.Clue,
             clueStartI);
       }

FinModelUtility/Fin/Fin.Picross/src/moves/CellMoves.cs

@@ -19,6 +19,7 @@ public enum PicrossCellMoveSource {
   EMPTY_BETWEEN_CLUES,
   EMPTY_AROUND_KNOWN_CLUE,
   EMPTY_UP_TO_FIRST_CLUE,
+  WITHIN_LAST_CLUE,
 }
 
 [Equatable]

FinModelUtility/Fin/Fin.Picross/src/moves/ClueMoves.cs

@@ -6,9 +6,10 @@ public enum PicrossClueMoveSource {
   FREEBIE_EMPTY,
   FREEBIE_FULL_LENGTH,
   FREEBIE_PERFECT_FIT,
-  FIRST_CLUE,
+  FIRST_CLUE_IN_LINE,
   ALL_CLUES_SOLVED,
   ONLY_MATCHING_CLUE,
+  LAST_UNSOLVED_CLUE,
 }
 
 [Equatable]

FinModelUtility/Fin/Fin.Picross/src/solver/LastClueSolverMethod.cs

@@ -0,0 +1,102 @@
+using fin.picross.moves;
+using fin.util.enumerables;
+
+namespace fin.picross.solver;
+
+public class LastClueSolverMethod : IPicrossSolverMethod {
+  public IEnumerable<IPicrossMove1d>
+      TryToFindMoves(IPicrossLineState lineState) {
+    // Make sure we only run this solver if there's a single unsolved clue
+    var clueStates = lineState.ClueStates;
+    var lastUnsolvedClue
+        = clueStates.FirstOrDefaultAndCount(c => !c.Solved,
+                                            out var unsolvedClueCount);
+    if (lastUnsolvedClue == null || unsolvedClueCount > 1) {
+      yield break;
+    }
+
+    var cellStates = lineState.CellStates;
+    var length = cellStates.Count;
+
+    int? firstUnclaimedFilledCellIndex = null;
+    int? lastUnclaimedFilledCellIndex = null;
+
+    // Find first and last unclaimed filled cells in row
+    for (var i = 0; i < length; ++i) {
+      var cellState = cellStates[i];
+      var isUnclaimed = cellState.Status == PicrossCellStatus.KNOWN_FILLED &&
+                        (lineState.IsColumn
+                            ? cellState.ColumnClue == null
+                            : cellState.RowClue == null);
+
+      if (!isUnclaimed) {
+        continue;
+      }
+
+      firstUnclaimedFilledCellIndex ??= i;
+      lastUnclaimedFilledCellIndex = i;
+    }
+
+    // If there are no unclaimed cells, there's nothing we can do
+    if (firstUnclaimedFilledCellIndex == null ||
+        lastUnclaimedFilledCellIndex == null) {
+      yield break;
+    }
+
+    // Fill in any cells between the first and last filled unclaimed cell
+    for (var i = firstUnclaimedFilledCellIndex.Value + 1;
+         i < lastUnclaimedFilledCellIndex.Value;
+         ++i) {
+      if (cellStates[i].Status == PicrossCellStatus.UNKNOWN) {
+        yield return new PicrossCellMove1d(
+            PicrossCellMoveType.MARK_FILLED,
+            PicrossCellMoveSource.WITHIN_LAST_CLUE,
+            i);
+      }
+    }
+
+    // Get the total accounted for length of the clue
+    var clueLength = lastUnsolvedClue.Length;
+    var filledLength = lastUnclaimedFilledCellIndex.Value -
+                       firstUnclaimedFilledCellIndex.Value +
+                       1;
+
+    // If it's already the full length, we're done!
+    if (clueLength == filledLength) {
+      yield break;
+    }
+
+    // Otherwise, we need to fill in cells that are too far away
+    var remainingClueLength = clueLength - filledLength;
+
+    var remainingClueLengthBefore = remainingClueLength;
+    for (var i = firstUnclaimedFilledCellIndex.Value - 1; i >= 0; --i) {
+      var cellStatus = cellStates[i].Status;
+      if (cellStatus == PicrossCellStatus.UNKNOWN) {
+        if (remainingClueLengthBefore-- <= 0) {
+          yield return new PicrossCellMove1d(
+              PicrossCellMoveType.MARK_EMPTY,
+              PicrossCellMoveSource.TOO_FAR_FROM_KNOWN,
+              i);
+        }
+      } else {
+        remainingClueLengthBefore = 0;
+      }
+    }
+
+    var remainingClueLengthAfter = remainingClueLength;
+    for (var i = lastUnclaimedFilledCellIndex.Value + 1; i < length; ++i) {
+      var cellStatus = cellStates[i].Status;
+      if (cellStatus == PicrossCellStatus.UNKNOWN) {
+        if (remainingClueLengthAfter-- <= 0) {
+          yield return new PicrossCellMove1d(
+              PicrossCellMoveType.MARK_EMPTY,
+              PicrossCellMoveSource.TOO_FAR_FROM_KNOWN,
+              i);
+        }
+      } else {
+        remainingClueLengthAfter = 0;
+      }
+    }
+  }
+}

FinModelUtility/Fin/Fin.Picross/src/solver/PicrossLineState.cs

@@ -1,11 +1,14 @@
 namespace fin.picross.solver;
 
 public interface IPicrossLineState {
+  bool IsColumn { get; }
   IReadOnlyList<IReadOnlyPicrossCellState> CellStates { get; }
   IReadOnlyList<IReadOnlyPicrossClueState> ClueStates { get; }
 }
 
 public class PicrossLineState : IPicrossLineState {
+  public required bool IsColumn { get; init; }
+
   public required IReadOnlyList<IReadOnlyPicrossCellState> CellStates {
     get;
     init;