tweaked nurikabe to be more reasonably difficult/generation speed trade of

Author: FelineStateMachine

nurikabe/generator.go

@@ -14,6 +14,7 @@ import (
 const (
 	generationHardTimeout        = 10 * time.Second
 	uniquenessMinRemainingBudget = 250 * time.Millisecond
+	frontierBiasSampleCount      = 7
 )
 
 type generationBudget struct {
@@ -677,12 +678,41 @@ func (s *candidateState) popFrontier(rng *rand.Rand) (point, bool) {
 	if len(s.frontier) == 0 {
 		return point{}, false
 	}
-	idx := rng.IntN(len(s.frontier))
-	picked := s.frontier[idx]
+
+	bestIdx := -1
+	bestScore := -1
+	samples := min(frontierBiasSampleCount, len(s.frontier))
+	for range samples {
+		idx := rng.IntN(len(s.frontier))
+		score := s.frontierPriorityScore(s.frontier[idx])
+		if score > bestScore || (score == bestScore && rng.IntN(2) == 0) {
+			bestScore = score
+			bestIdx = idx
+		}
+	}
+
+	if bestIdx < 0 {
+		bestIdx = rng.IntN(len(s.frontier))
+	}
+
+	picked := s.frontier[bestIdx]
 	s.removeFrontier(picked)
 	return picked, true
 }
 
+func (s *candidateState) frontierPriorityScore(p point) int {
+	if !s.inBounds(p) || s.sea[p.y][p.x] {
+		return 0
+	}
+
+	label := s.labels[p.y][p.x]
+	componentSize := s.componentSize[label]
+	sameLabelNeighbors := len(s.landNeighborsWithLabel(p, label))
+
+	// Favor carving from larger components; local degree nudges toward useful splits.
+	return componentSize*16 + sameLabelNeighbors*3
+}
+
 func (s *candidateState) removeComponent(label int) {
 	size, ok := s.componentSize[label]
 	if !ok {
@@ -1048,7 +1078,7 @@ func modeIslandProfile(mode NurikabeMode) islandProfile {
 			minAverageSize:    1.8,
 			maxSingletonRatio: 0.72,
 			minLargestIsland:  4,
-			maxLargestIsland:  20,
+			maxLargestIsland:  15,
 		}
 	case "Expert":
 		return islandProfile{
@@ -1059,7 +1089,7 @@ func modeIslandProfile(mode NurikabeMode) islandProfile {
 			minAverageSize:    1.7,
 			maxSingletonRatio: 0.78,
 			minLargestIsland:  4,
-			maxLargestIsland:  22,
+			maxLargestIsland:  17,
 		}
 	default:
 		return islandProfile{

nurikabe/nurikabe_test.go

@@ -590,10 +590,23 @@ func TestConstructedCandidateValidCompletedBoard(t *testing.T) {
 		clueTarget = 2
 	}
 
-	rng := rand.New(rand.NewPCG(901, 1777))
-	candidate, err := buildCandidateByCarving(mode, clueTarget, profile, rng, 0)
+	var (
+		candidate candidateResult
+		err       error
+	)
+
+	// Keep this deterministic while avoiding reliance on a single RNG path.
+	for attempt := range 24 {
+		seedA := uint64(901 + attempt*17)
+		seedB := uint64(1777 + attempt*29)
+		rng := rand.New(rand.NewPCG(seedA, seedB))
+		candidate, err = buildCandidateByCarving(mode, clueTarget, profile, rng, attempt)
+		if err == nil {
+			break
+		}
+	}
 	if err != nil {
-		t.Fatalf("buildCandidateByCarving error: %v", err)
+		t.Fatalf("buildCandidateByCarving failed across deterministic attempts: %v", err)
 	}
 
 	if err := validateClues(candidate.puzzle.Clues, candidate.puzzle.Width, candidate.puzzle.Height); err != nil {