Refactored BruteForceSolver for better readability

src/main/kotlin/io/github/ilikeyourhat/kudoku/Kudoku.kt

@@ -8,6 +8,7 @@ import io.github.ilikeyourhat.kudoku.rating.DeductionBasedRater
 import io.github.ilikeyourhat.kudoku.rating.Difficulty
 import io.github.ilikeyourhat.kudoku.solving.SolutionCount
 import io.github.ilikeyourhat.kudoku.solving.SudokuSolver
+import io.github.ilikeyourhat.kudoku.solving.bruteforce.BruteForceSolver
 import io.github.ilikeyourhat.kudoku.solving.sat.SatSolver
 import io.github.ilikeyourhat.kudoku.type.BUILD_IN_TYPES
 import kotlin.random.Random
@@ -25,6 +26,10 @@ object Kudoku {
         return SatSolver()
     }
 
+    fun bruteForceSolver(): SudokuSolver {
+        return BruteForceSolver()
+    }
+
     fun create(
         type: SudokuType,
         difficulty: Difficulty? = null,

src/main/kotlin/io/github/ilikeyourhat/kudoku/model/SudokuType.kt

@@ -6,8 +6,8 @@ interface SudokuType {
     val name: String
     val sizeX: Int
     val sizeY: Int
-    val possibleValues: Int
+    val maxValue: Int
     fun template(): String
     fun divider(): RegionDivider
-    fun allPossibleValues(): List<Int> = IntRange(1, possibleValues).toList()
+    fun allPossibleValues(): List<Int> = IntRange(1, maxValue).toList()
 }

src/main/kotlin/io/github/ilikeyourhat/kudoku/solving/bruteforce/BruteForceSolver.kt

@@ -1,100 +1,66 @@
-@file:Suppress("UnsafeCallOnNullableType")
-
 package io.github.ilikeyourhat.kudoku.solving.bruteforce
 
 import io.github.ilikeyourhat.kudoku.model.Field
-import io.github.ilikeyourhat.kudoku.model.Point
-import io.github.ilikeyourhat.kudoku.model.Region
 import io.github.ilikeyourhat.kudoku.model.Sudoku
+import io.github.ilikeyourhat.kudoku.model.SudokuType
 import io.github.ilikeyourhat.kudoku.solving.SudokuSolver
+import kotlin.random.Random
 
-class BruteForceSolver : SudokuSolver {
-
-    internal enum class Direction {
-        FORWARD, BACKWARD
-    }
+class BruteForceSolver(
+    private val random: Random? = null
+) : SudokuSolver {
 
     override fun solve(sudoku: Sudoku): Sudoku {
-        return Command(sudoku).findSolution()
+        val result = sudoku.copy()
+        val lookup = RegionLookup(result)
+        val fields = result.allFields
+            .filter { it.isEmpty }
+            .applyRandomOrder()
+
+        runAlgorithm(result.type, fields, lookup)
+        return result
     }
 
-    private class Command(private val origin: Sudoku) {
-        private val sudoku: Sudoku = origin.copy()
-        private val regionLookup: Map<Point, List<Region>> = createRegionLookup(sudoku)
-        private val iterator: ListIterator<Field> = sudoku.allFields.listIterator()
-
-        private var currentDirection = Direction.FORWARD
-        private lateinit var currentField: Field
-
-        fun findSolution(): Sudoku {
-            while (canMove()) {
-                move()
-                if (isOriginFieldEmpty()) {
-                    setNextValuesAndCheckGrid()
+    private fun runAlgorithm(
+        type: SudokuType,
+        fields: List<Field>,
+        lookup: RegionLookup
+    ) {
+        var position = 0
+        loop@ while (fields.indices.contains(position)) {
+            val field = fields[position]
+            for (value in field.value..<type.maxValue) {
+                field.set(value + 1)
+                if (lookup.isGridCorrectAfterChange(field)) {
+                    position++
+                    continue@loop
                 }
             }
-            return sudoku
-        }
-
-        private fun canMove(): Boolean {
-            return canMoveForward() || canMoveBackward()
-        }
-
-        private fun canMoveForward(): Boolean {
-            return currentDirection == Direction.FORWARD && iterator.hasNext()
-        }
-
-        private fun canMoveBackward(): Boolean {
-            return currentDirection == Direction.BACKWARD && iterator.hasPrevious()
-        }
-
-        private fun move() {
-            currentField = if (currentDirection == Direction.FORWARD) {
-                iterator.next()
-            } else {
-                iterator.previous()
-            }
+            field.clear()
+            position--
         }
+    }
 
-        private fun changeDirection(newDirection: Direction) {
-            if (currentDirection != newDirection) {
-                currentDirection = newDirection
-                /*
-                 * Alternating calls to ListIterator.next() and ListIterator.previous() will return the same element
-                 * repeatedly. So to compensate this and return the real next/previous element in the next move, we must
-                 * move one step further after every direction change.
-                 */
-                move()
-            }
+    private fun List<Field>.applyRandomOrder(): List<Field> {
+        return if (random != null) {
+            this.shuffled(random)
+        } else {
+            this
         }
+    }
 
-        private fun isOriginFieldEmpty(): Boolean {
-            val x = currentField.x
-            val y = currentField.y
-            return origin.atField(x, y).isEmpty
-        }
+    private class RegionLookup(sudoku: Sudoku) {
 
-        private fun setNextValuesAndCheckGrid() {
-            val currentNumber = currentField.value()
-            for (i in currentNumber + 1..sudoku.type.possibleValues) {
-                currentField.set(i)
-                if (isGridCorrectAfterChange()) {
-                    changeDirection(Direction.FORWARD)
-                    return
+        private val regionsMap = sudoku.allFields
+            .associate { field ->
+                field.position to sudoku.regions.filter { region ->
+                    region.contains(field)
                 }
             }
-            currentField.clear()
-            changeDirection(Direction.BACKWARD)
-        }
 
-        private fun isGridCorrectAfterChange(): Boolean {
-            return regionLookup.getValue(currentField.position)
+        fun isGridCorrectAfterChange(field: Field): Boolean {
+            return regionsMap.getValue(field.position)
                 .all { it.isValid() }
         }
-
-        private fun createRegionLookup(sudoku: Sudoku): Map<Point, List<Region>> {
-            return sudoku.allFields
-                .associate { field -> field.position to sudoku.regions.filter { it.contains(field) } }
-        }
     }
 }

src/main/kotlin/io/github/ilikeyourhat/kudoku/solving/deduction/solver/DeductionSolverV2.kt

@@ -15,7 +15,7 @@ class DeductionSolverV2 : DeductionSolver() {
             NakedSinglesAlgorithm.Factory(),
             HiddenSinglesAlgorithm.Factory()
         )
-        for (i in 2..type.possibleValues / 2) {
+        for (i in 2..type.maxValue / 2) {
             algorithms.add(NakedValuesAlgorithm.Factory(i))
             algorithms.add(HiddenValuesAlgorithm.Factory(i))
         }

src/main/kotlin/io/github/ilikeyourhat/kudoku/solving/deduction/solver/DeductionSolverV3.kt

@@ -17,7 +17,7 @@ class DeductionSolverV3 : DeductionSolver() {
             NakedSinglesAlgorithm.Factory(),
             HiddenSinglesAlgorithm.Factory()
         )
-        for (i in 2..type.possibleValues / 2) {
+        for (i in 2..type.maxValue / 2) {
             algorithms.add(NakedValuesAlgorithm.Factory(i))
             algorithms.add(HiddenValuesAlgorithm.Factory(i))
         }

src/main/kotlin/io/github/ilikeyourhat/kudoku/solving/sat/SatSolver.kt

@@ -18,7 +18,7 @@ class SatSolver : SudokuSolver, SudokuSolutionChecker {
 
     private class Command(private val sudoku: Sudoku) {
 
-        private val indexEncoder = IndexEncoder(sudoku.sizeX(), sudoku.sizeY(), sudoku.type.possibleValues)
+        private val indexEncoder = IndexEncoder(sudoku.sizeX(), sudoku.sizeY(), sudoku.type.maxValue)
         private val engine = SatEngine()
 
         fun solve(): Sudoku {
@@ -61,7 +61,7 @@ class SatSolver : SudokuSolver, SudokuSolutionChecker {
         }
 
         private fun addCausesForRegions(sudoku: Sudoku) {
-            for (possibleValue in 1..sudoku.type.possibleValues) {
+            for (possibleValue in 1..sudoku.type.maxValue) {
                 for (region in sudoku.regions) {
                     val list = mutableListOf<Int>()
                     for ((position) in region) {
@@ -75,7 +75,7 @@ class SatSolver : SudokuSolver, SudokuSolutionChecker {
 
         private fun createValues(field: Field): List<Int> {
             val list = mutableListOf<Int>()
-            for (value in 1..sudoku.type.possibleValues) {
+            for (value in 1..sudoku.type.maxValue) {
                 val index = indexEncoder.encode(field.position(), value)
                 list.add(index)
             }

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Butterfly12x12.kt

@@ -8,7 +8,7 @@ object Butterfly12x12 : SudokuType {
     override val name = "butterfly_12x12"
     override val sizeX = 12
     override val sizeY = 12
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun divider(): RegionDivider {
         return RegionDivider()

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic16x16.kt

@@ -8,7 +8,7 @@ object Classic16x16 : SudokuType {
     override val name = "classic_16x16"
     override val sizeX = 16
     override val sizeY = 16
-    override val possibleValues = 16
+    override val maxValue = 16
 
     override fun template() = """
         _,_,_,_ _,_,_,_ _,_,_,_ _,_,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic25x25.kt

@@ -8,7 +8,7 @@ object Classic25x25 : SudokuType {
     override val name = "classic_25x25"
     override val sizeX = 25
     override val sizeY = 25
-    override val possibleValues = 25
+    override val maxValue = 25
 
     override fun template() = """
         _,_,_,_,_ _,_,_,_,_ _,_,_,_,_ _,_,_,_,_ _,_,_,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic4x4.kt

@@ -8,7 +8,7 @@ object Classic4x4 : SudokuType {
     override val name = "classic_4x4"
     override val sizeX = 4
     override val sizeY = 4
-    override val possibleValues = 4
+    override val maxValue = 4
 
     override fun template() = """
         _,_ _,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic6x6Horizontal.kt

@@ -8,7 +8,7 @@ object Classic6x6Horizontal : SudokuType {
     override val name = "classic_6x6_horizontal"
     override val sizeX = 6
     override val sizeY = 6
-    override val possibleValues = 6
+    override val maxValue = 6
 
     override fun template() = """
         _,_,_ _,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic6x6Vertical.kt

@@ -8,7 +8,7 @@ object Classic6x6Vertical : SudokuType {
     override val name = "classic_6x6_vertical"
     override val sizeX = 6
     override val sizeY = 6
-    override val possibleValues = 6
+    override val maxValue = 6
 
     override fun template() = """
         _,_ _,_ _,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Classic9x9.kt

@@ -8,7 +8,7 @@ object Classic9x9 : SudokuType {
     override val name = "classic_9x9"
     override val sizeX = 9
     override val sizeY = 9
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         _,_,_ _,_,_ _,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/DoubleBackslash15x15.kt

@@ -8,7 +8,7 @@ object DoubleBackslash15x15 : SudokuType {
     override val name = "double_backslash_15x15"
     override val sizeX = 15
     override val sizeY = 15
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         _,_,_ _,_,_ _,_,_ #,#,# #,#,#

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/DoubleDiagonal9x9.kt

@@ -8,7 +8,7 @@ object DoubleDiagonal9x9 : SudokuType {
     override val name = "double_diagonal_9x9"
     override val sizeX = 9
     override val sizeY = 9
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = Classic9x9.template()
 

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/DoubleSlash15x15.kt

@@ -8,7 +8,7 @@ object DoubleSlash15x15 : SudokuType {
     override val name = "double_slash_15x15"
     override val sizeX = 15
     override val sizeY = 15
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         #,#,# #,#,# _,_,_ _,_,_ _,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/SamuraiButterfly30x30.kt

@@ -8,7 +8,7 @@ object SamuraiButterfly30x30 : SudokuType {
     override val name = "samurai_butterfly_30x30"
     override val sizeX = 30
     override val sizeY = 30
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         _,_,_ _,_,_ _,_,_ _,_,_ #,#,# #,#,# _,_,_ _,_,_ _,_,_ _,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/SamuraiClassic21x21.kt

@@ -8,7 +8,7 @@ object SamuraiClassic21x21 : SudokuType {
     override val name = "samurai_classic_21x21"
     override val sizeX = 21
     override val sizeY = 21
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         _,_,_ _,_,_ _,_,_ #,#,# _,_,_ _,_,_ _,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/SamuraiClassic40x40.kt

@@ -8,7 +8,7 @@ object SamuraiClassic40x40 : SudokuType {
     override val name = "samurai_classic_40x40"
     override val sizeX = 40
     override val sizeY = 40
-    override val possibleValues = 16
+    override val maxValue = 16
 
     override fun template() = """
         _,_,_,_ _,_,_,_ _,_,_,_ _,_,_,_ #,#,#,# #,#,#,# _,_,_,_ _,_,_,_ _,_,_,_ _,_,_,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Square1x1.kt

@@ -8,7 +8,7 @@ object Square1x1 : SudokuType {
     override val name = "square_1x1"
     override val sizeX = 1
     override val sizeY = 1
-    override val possibleValues = 1
+    override val maxValue = 1
 
     override fun divider(): RegionDivider {
         return RegionDivider()

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/Square2x2.kt

@@ -8,7 +8,7 @@ object Square2x2 : SudokuType {
     override val name = "square_2x2"
     override val sizeX = 2
     override val sizeY = 2
-    override val possibleValues = 2
+    override val maxValue = 2
 
     override fun template() = """
         _,_

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/TripleBackslash15x15.kt

@@ -8,7 +8,7 @@ object TripleBackslash15x15 : SudokuType {
     override val name = "triple_backslash_15x15"
     override val sizeX = 15
     override val sizeY = 15
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         _,_,_ _,_,_ _,_,_ #,#,# #,#,#

src/main/kotlin/io/github/ilikeyourhat/kudoku/type/TripleSlash15x15.kt

@@ -8,7 +8,7 @@ object TripleSlash15x15 : SudokuType {
     override val name = "triple_slash_15x15"
     override val sizeX = 15
     override val sizeY = 15
-    override val possibleValues = 9
+    override val maxValue = 9
 
     override fun template() = """
         #,#,# #,#,# _,_,_ _,_,_ _,_,_