Minor improvements to the solver

cleanup code and improve performance

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 {
@@ -21,10 +19,18 @@ fun generateGame(size: Int = 6): Game {
 
     var i = 0
 
+    // Run your solver on the reduced set of clues and count the number of possible solutions.
+
+    // First do a binary search until the game isn't solvable anymore for the first time.
+    var halvedClues = clues.take(clues.size / 2)
+    while (solve(grid.toGrid(), halvedClues) == SOLVABLE) {
+        clues = halvedClues
+        halvedClues = clues.take(clues.size / 2)
+    }
+    // With the last solvable clues set, see what clues can be removed while the game is still solvable.
     // If i >= n, we are done. The set of clues is minimal.
     while (i < clues.size) {
         // Run your solver on the reduced set of clues and count the number of possible solutions.
-        // TODO: first do binary search
         val temp = clues - clues[i]
         if (solve(grid.toGrid(), temp) == SOLVABLE) {
             // If there is exactly one solution, update clues and reset index.
@@ -33,27 +39,17 @@ fun generateGame(size: Int = 6): Game {
         }
         i++
     }
-    return Game(grid.toGrid(), clues)
 
-    // (You can speed this up by removing clues in batches rather than one at a time, but it makes the algorithm more complicated to describe.)
+    return Game(grid.toGrid(), clues)
 }
 
 internal fun solve(
     grid: Grid,
     clues: Collection<Clue>
 ): PuzzleSolution {
-    // Start with a grid where each cell is a list of all possible items.
-
-    // First, set the positions of the items that are already known.
-//    clues.filterIsInstance<PositionClue<ItemClass<*>>>().forEach { position ->
-//        position.removeForbiddenOptions(grid)
-//    }
-//    grid.forEach { row -> row.forEach { cell -> row.cleanupOptions(cell) } }
-
     // For each clue, remove any items that violate the clue.
     // If any cell has only one item left, remove that item from all other cells.
     // Repeat until no more items can be removed.
-//    val otherClues = clues.filter { it !is PositionClue<*> }
     var removedOptions: Boolean
     do {
         removedOptions = false
@@ -66,9 +62,6 @@ internal fun solve(
         }
         // TODO clean up groups in rows (?)
         grid.forEach { row -> row.forEach { cell -> row.cleanupOptions(cell) } }
-//        grid.forEach { row ->
-//            removedOptions = row.tryOptionsForClues(grid, otherClues) || removedOptions
-//        }
     } while (removedOptions)
 
     // If any cell has no items left, the puzzle has no solution.
@@ -77,16 +70,6 @@ internal fun solve(
     // If all cells have exactly one item left, the puzzle is solved.
     if (grid.cells.all { 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.
-//    return if (
-//        grid.cells
-//            .filter { it.selection == null }
-//            .any { it.countSolutions(grid, clues) == 1 }
-//    ) {
-//        SOLVABLE
-//    } else {
-//        MULTIPLE_SOLUTIONS
-//    }
     return MULTIPLE_SOLUTIONS
 }
 

domain/src/test/kotlin/ch/dissem/yaep/domain/GameTest.kt

@@ -1,14 +1,8 @@
 package ch.dissem.yaep.domain
 
-import ch.dissem.yaep.domain.Animal.ANT
-import ch.dissem.yaep.domain.Animal.OCTOPUS
-import ch.dissem.yaep.domain.Animal.SNAIL
-import ch.dissem.yaep.domain.Nationality.CANADA
-import ch.dissem.yaep.domain.Nationality.SWITZERLAND
-import ch.dissem.yaep.domain.Nationality.UKRAINE
-import ch.dissem.yaep.domain.Profession.ASTRONAUT
-import ch.dissem.yaep.domain.Profession.FARMER
-import ch.dissem.yaep.domain.Profession.SOFTWARE_DEV
+import ch.dissem.yaep.domain.Animal.*
+import ch.dissem.yaep.domain.Nationality.*
+import ch.dissem.yaep.domain.Profession.*
 import ch.dissem.yaep.domain.PuzzleSolution.SOLVABLE
 import ch.tutteli.atrium.api.fluent.en_GB.feature
 import ch.tutteli.atrium.api.fluent.en_GB.toBeGreaterThan
@@ -16,7 +10,7 @@ import ch.tutteli.atrium.api.fluent.en_GB.toBeLessThan
 import ch.tutteli.atrium.api.fluent.en_GB.toEqual
 import ch.tutteli.atrium.api.verbs.expect
 import kotlin.test.Test
-import kotlin.time.Duration.Companion.seconds
+import kotlin.time.Duration.Companion.milliseconds
 import kotlin.time.measureTime
 
 class GameTest {
@@ -36,8 +30,9 @@ class GameTest {
             }
         }
         println("Clues: ${game.clues.size}")
+        println("Time: $time")
         expect(solve(game.grid, game.clues)).toEqual(SOLVABLE)
-        expect(time).toBeLessThan(1.seconds)
+        expect(time).toBeLessThan(500.milliseconds)
     }
 
     @Test