Minor improvements to the solver

domain/src/main/kotlin/ch/dissem/yaep/domain/Grid.kt

@@ -19,6 +19,14 @@ class Grid(
         return this[item.itemType.companion].first { it.selection == item }
     }
 
+    fun anyCell(predicate: (GameCell<ItemClass<*>>) -> Boolean): Boolean {
+        return flatMap { it }.any(predicate)
+    }
+
+    fun allCells(predicate: (GameCell<ItemClass<*>>) -> Boolean): Boolean {
+        return flatMap { it }.all(predicate)
+    }
+
     override fun toString(): String {
         return joinToString("\n") { row ->
             row.joinToString("") { it.selection?.symbol ?: "  " }

domain/src/main/kotlin/ch/dissem/yaep/domain/generator.kt

@@ -1,8 +1,6 @@
 package ch.dissem.yaep.domain
 
-import ch.dissem.yaep.domain.PuzzleSolution.MULTIPLE_SOLUTIONS
-import ch.dissem.yaep.domain.PuzzleSolution.NO_SOLUTION
-import ch.dissem.yaep.domain.PuzzleSolution.SOLVABLE
+import ch.dissem.yaep.domain.PuzzleSolution.*
 import kotlin.random.Random
 
 fun generateGame(size: Int = 6): Game {
@@ -64,12 +62,10 @@ internal fun solve(
     } while (removedOptions)
 
     // If any cell has no items left, the puzzle has no solution.
-    if (grid.flatMap { it }.any { cell -> cell.options.isEmpty() }) {
-        return NO_SOLUTION
-    }
+    if (grid.anyCell { cell -> cell.options.isEmpty() }) return NO_SOLUTION
 
     // If all cells have exactly one item left, the puzzle is solved.
-    if (grid.flatMap { it }.all { it.selection != null }) return SOLVABLE
+    if (grid.allCells { it.selection != null }) return SOLVABLE
 
     // If there are still cells with multiple items, pick one and try each item in turn, then go back to step 2.
     for (i in 0 until grid.size) {
@@ -88,6 +84,7 @@ internal fun solve(
             }
         }
     }
+    // This shouldn't happen, as we don't check if there are more solutions once we find one
     return MULTIPLE_SOLUTIONS
 }