Some change made, dunno what.

src/main/kotlin/be/nielandt/CrossSolver.kt

@@ -7,9 +7,9 @@ open abstract class CrossSolver {
     /**
      * Solve all crosses, look for a minimal set of moves for each color's cross.
      */
-    abstract fun solveCrosses(edgeModel: EdgeModel): Map<Int, List<Int>>
+    abstract fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray>
 
-    fun solveCrossesTimed(edgeModel: EdgeModel): Map<Int, List<Int>> {
+    fun solveCrossesTimed(edgeModel: EdgeModel): Map<Int, IntArray> {
         val now = Instant.now()
         val solveCrosses = solveCrosses(edgeModel)
         val between = Duration.between(now, Instant.now())
@@ -18,7 +18,7 @@ open abstract class CrossSolver {
     }
 
     companion object {
-        fun printResults(results: Map<Int, List<Int>>) {
+        fun printResults(results: Map<Int, IntArray>) {
             println("results: ")
             results.forEach { color, moveList ->
                 println("> color ${colorLetter(color)}, moves (${moveList.size}) ${moveList.map { it -> decodeMove(it) }}")
@@ -29,64 +29,40 @@ open abstract class CrossSolver {
 
 /**
  * Let's look for symmetries.
+ *
+ * - no changes: base times:                        72s, 29s, 61s
+ * - changed list<int> in edgemodel to intarray:    51s, 21s, 35s
+ * - new version, optimised now avoid recalc:       47s, 21s, 34s, 14s,  (401592291, 147023415, 67382002, 67381995)
  */
 fun main(args: Array<String>) {
+    /**
+     * choose your moves, fixed or random?
+     */
+//    val moves = parseMoves("U2 F2 U2 D R2 F2 R2 B2 U' D2 L B L2 U2 L B' U L R B".replace('\'', '_'))
+    val moves = randomMoves(20)
 
-//    val u2 = Move.U2
-//    val doMove = edgeModel.doMove(Move.U2)
-//    println(u2)
-//    println(doMove)
-//    println("doMove.whiteCrossSolved() = ${doMove.whiteCrossSolved()}")
-
-//    val message = EdgeModel().doMoves(Move.R, Move.U, Move.R_)
-//    println(message)
-//    println("message.whiteCrossSolved() = ${message.whiteCrossSolved()}")
-//
-//    val doMoves = EdgeModel().doMoves(Move.random(15))
-//    println("random 15 moves = ${doMoves}")
-//    println("doMoves.whiteCrossSolved() = ${doMoves.whiteCrossSolved()}")
-
-
-//    val begin = Instant.now()
-//    var i: Long = 0
-//    while (Duration.between(begin, Instant.now()) < Duration.ofMinutes(1)) {
-//        EdgeModel().doMoves(Move.random(15))
-//        i++
-//    }
-//    println("i = ${i}")
-//
-//    val counter = Counter(4, 3)
-//    while (counter.increase()) {
-//        println("counter = ${counter}")
-//    }
-
-
-    // do a fixed scramble for testing purposes
-    // noskip Move.enum 30s, skip Move.enum 32s
-    val fixedMoves = parseMoves("L_, D, U, L2, F, D, B, D, U2, D, B_, F2, D2, U_, R, D2, R_, L, B_, R")
-    println("fixedMoves = ${fixedMoves}")
-    // scramble random
-    val randomMoves = randomMoves(20)
-
-    val moves = fixedMoves
     println("Scramble: ${moves.map { decodeMove(it) }}")
 
-
-    val usedModel = EdgeModel(moves)
+    val usedModel = EdgeModel.withMoves(moves)
     println(usedModel)
 
-//    val baseSolve = CrossSolverBase().solveCrossesTimed(usedModel)
-//    CrossSolver.printResults(baseSolve)
-
-    val upgradedSolve = CrossSolverUpgraded().solveCrossesTimed(usedModel)
-    CrossSolver.printResults(upgradedSolve)
+//    val upgradedSolve = CrossSolverUpgraded().solveCrossesTimed(usedModel)
+//    CrossSolver.printResults(upgradedSolve)
 //
-    val upgradedSolveSkip = CrossSolverUpgradedSkip().solveCrossesTimed(usedModel)
-    CrossSolver.printResults(upgradedSolveSkip)
+//    val upgradedSolveSkip = CrossSolverUpgradedSkip().solveCrossesTimed(usedModel)
+//    CrossSolver.printResults(upgradedSolveSkip)
+//
+//    val solveCrossesTimed = CrossSolverIterator().solveCrossesTimed(usedModel)
+//    CrossSolver.printResults(solveCrossesTimed)
+
+    val s3 = CrossSolverIteratorUpgraded().solveCrossesTimed(usedModel)
+    CrossSolver.printResults(s3)
 
 //    val allCrossMoveCountUpgradedSkip = allCrossMoveCountUpgradedSkip(scrambledModel)
 //    allCrossMoveCountUpgradedSkip.forEach { color, moves ->
 //        println("skip upgrade cross for color: ${color} in ${moves.size}: ${moves.joinToString(" ")}")
 //    }
+//    val baseSolve = CrossSolverBase().solveCrossesTimed(usedModel)
+//    CrossSolver.printResults(baseSolve)
 }
 

src/main/kotlin/be/nielandt/CrossSolverBase.kt

@@ -1,14 +1,13 @@
 package be.nielandt
 
-import be.nielandt.counter.CounterBasic
 import be.nielandt.counter.CounterTieredFactory
 
 class CrossSolverBase : CrossSolver() {
     /**
      * Solve the minimal cross for all colors.
      */
-    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, List<Int>> {
-        val moveCounts = mutableMapOf<Int, List<Int>>()
+    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray> {
+        val moveCounts = mutableMapOf<Int, IntArray>()
 
         for (moveCount in 1..8) {
             // build a counter of moveCount big
@@ -24,7 +23,7 @@ class CrossSolverBase : CrossSolver() {
                     if (!moveCounts.containsKey(color)) {
                         val crossSolved = afterMoves.crossSolved(color)
                         if (crossSolved) {
-                            moveCounts[color] = counter.counter.toList()
+                            moveCounts[color] = counter.counter.copyOf()
                         }
                     }
                 }

src/main/kotlin/be/nielandt/CrossSolverIterator.kt

@@ -0,0 +1,54 @@
+package be.nielandt
+
+import be.nielandt.iterator.ValidClassMoveIterator
+
+class CrossSolverIterator : CrossSolver() {
+    /**
+     * Solve the minimal cross for all colors.
+     */
+    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray> {
+        val moveCounts = mutableMapOf<Int, IntArray>()
+        var iteratorCount = 0
+
+        for (moveCount in 1..8) {
+            // build a counter of moveCount big
+            println("crossSolverIterator doing $moveCount")
+            val iterator = ValidClassMoveIterator(moveCount)
+
+            // count up, each state of the counter corresponds to a combination of moves
+            while (iterator.hasNext()) {
+                val moves = iterator.next()
+                iteratorCount++
+                // execute the moves
+                val afterMoves = edgeModel.doMoves(moves.toList())
+                // check crosses that have not been found yet
+                (0..5).forEach { color ->
+                    if (!moveCounts.containsKey(color)) {
+                        val crossSolved = afterMoves.crossSolved(color)
+                        if (crossSolved) {
+                            moveCounts[color] = moves
+                        }
+                    }
+                }
+                if (moveCounts.keys.size == 6) {
+                    println("iteratorCount = ${iteratorCount}")
+                    return@solveCrosses moveCounts
+                }
+            }
+        }
+
+        println("iteratorCount = ${iteratorCount}")
+
+        return moveCounts
+    }
+
+}
+
+fun main(args: Array<String>) {
+    val start = EdgeModel.solved().doMoves(randomMoves(20))
+    val solver = CrossSolverIterator()
+    val solveCrossesTimed = solver.solveCrossesTimed(start)
+    solveCrossesTimed.forEach { t, u ->
+        println("t $t u ${u.map { decodeMove(it) }}")
+    }
+}

src/main/kotlin/be/nielandt/CrossSolverIteratorUpgraded.kt

@@ -0,0 +1,44 @@
+package be.nielandt
+
+import be.nielandt.iterator.ValidClassMoveIterator
+
+/**
+ * This solver avoids redoing edgemodel manipulations. Should be equivalent to X nested for loops.
+ */
+class CrossSolverIteratorUpgraded : CrossSolver() {
+
+    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray> {
+        val moveCounts = mutableMapOf<Int, IntArray>()
+        var iteratorCount = 0
+        for (moveCount in 1..8) {
+            println("all cross move count upgrade doing $moveCount")
+            // build a counter of moveCount big
+            val counter = ValidClassMoveIterator(moveCount)
+            val edgeModelFactory = EdgeModelFactoryIterator(edgeModel, counter)
+
+            while (edgeModelFactory.hasNext()) {
+                // get the next model, using the internal counter which simply iterates over possible combinations of moves
+                val next = edgeModelFactory.getNext()
+                iteratorCount++
+
+                // check crosses that have not been found yet
+                (0..5).forEach { color ->
+                    if (!moveCounts.containsKey(color)) {
+                        val crossSolved = next.crossSolved(color)
+                        if (crossSolved) {
+                            // what is the move combination we're looking at?
+                            moveCounts[color] = edgeModelFactory.movesOfCurrent().copyOf()
+                        }
+                    }
+                }
+                // break if we have found hem all
+                if (moveCounts.keys.size == 6) {
+                    println("iteratorCount = $iteratorCount")
+                    return moveCounts
+                }
+            }
+        }
+        println("had to do it all... iteratorCount = $iteratorCount")
+        return moveCounts
+    }
+}

src/main/kotlin/be/nielandt/CrossSolverUpgraded.kt

@@ -7,8 +7,9 @@ import be.nielandt.counter.CounterBasic
  */
 class CrossSolverUpgraded : CrossSolver() {
 
-    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, List<Int>> {
-        val moveCounts = mutableMapOf<Int, List<Int>>()
+    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray> {
+        val moveCounts = mutableMapOf<Int, IntArray>()
+        var iteratorCount = 0
         for (moveCount in 1..8) {
             println("all cross move count upgrade doing $moveCount")
             // build a counter of moveCount big
@@ -18,6 +19,7 @@ class CrossSolverUpgraded : CrossSolver() {
             while (edgeModelFactory.hasNext()) {
                 // get the next model, using the internal counter which simply iterates over possible combinations of moves
                 val next = edgeModelFactory.getNext()
+                iteratorCount++
 
                 // check crosses that have not been found yet
                 (0..5).forEach { color ->
@@ -25,16 +27,18 @@ class CrossSolverUpgraded : CrossSolver() {
                         val crossSolved = next.crossSolved(color)
                         if (crossSolved) {
                             // what is the move combination we're looking at?
-                            moveCounts[color] = counter.counter.toList()
+                            moveCounts[color] = counter.counter.copyOf()
                         }
                     }
                 }
                 // break if we have found hem all
                 if (moveCounts.keys.size == 6) {
+                    println("iteratorCount = ${iteratorCount}")
                     return moveCounts
                 }
             }
         }
+        println("iteratorCount = ${iteratorCount}")
         return moveCounts
     }
 }

src/main/kotlin/be/nielandt/CrossSolverUpgradedSkip.kt

@@ -7,8 +7,9 @@ import be.nielandt.counter.CounterSkip
  */
 class CrossSolverUpgradedSkip : CrossSolver() {
 
-    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, List<Int>> {
-        val moveCounts = mutableMapOf<Int, List<Int>>()
+    override fun solveCrosses(edgeModel: EdgeModel): Map<Int, IntArray> {
+        val moveCounts = mutableMapOf<Int, IntArray>()
+        var iteratorCount = 0
         for (moveCount in 1..8) {
             println("all cross move count upgrade doing $moveCount")
             // build a counter of moveCount big
@@ -18,6 +19,7 @@ class CrossSolverUpgradedSkip : CrossSolver() {
             while (edgeModelFactory.hasNext()) {
                 // get the next model, using the internal counter which simply iterates over possible combinations of moves
                 val next = edgeModelFactory.getNext()
+                iteratorCount++
 
                 // check crosses that have not been found yet
                 (0..5).forEach { color ->
@@ -25,16 +27,18 @@ class CrossSolverUpgradedSkip : CrossSolver() {
                         val crossSolved = next.crossSolved(color)
                         if (crossSolved) {
                             // what is the move combination we're looking at?
-                            moveCounts[color] = counter.counter.toList()
+                            moveCounts[color] = counter.counter.copyOf()
                         }
                     }
                 }
                 // break if we have found hem all
                 if (moveCounts.keys.size == 6) {
+                    println("iteratorCount = ${iteratorCount}")
                     return moveCounts
                 }
             }
         }
+        println("iteratorCount = ${iteratorCount}")
         return moveCounts
 
     }

src/main/kotlin/be/nielandt/EdgeModel.kt

@@ -26,51 +26,17 @@ package be.nielandt
 
 class EdgeModel {
 
-    val model: Array<Int>
+    lateinit var model: IntArray
 
-    private val F_indices = intArrayOf(13, 18, 7, 20, 3, 0, 1, 2)
-    private val B_indices = intArrayOf(8, 9, 10, 11, 16, 15, 22, 5)
-    private val L_indices = intArrayOf(3, 23, 9, 19, 12, 13, 14, 15)
-    private val U_indices = intArrayOf(16, 17, 18, 19, 0, 12, 8, 4)
-    private val D_indices = intArrayOf(2, 6, 10, 14, 20, 21, 22, 23)
-    private val R_indices = intArrayOf(4, 5, 6, 7, 1, 17, 11, 21)
+    /**
+     * Create an edgemodel through the companion object.
+     */
+    private constructor()
 
-    constructor() {
-        // do a sanity check
-        val entries = mutableListOf(F_indices, B_indices, L_indices, U_indices, D_indices, R_indices).flatMap { it.asList() }.groupBy { it }.entries
-//        println("entries = ${entries}")
-        if (entries.any {
-                    it.value.size != 2
-                }) {
-            throw RuntimeException("each index should occur exactly twice in the arrays")
+    fun copyOf(model: EdgeModel): EdgeModel {
+        return EdgeModel.withModel(model.model)
     }
 
-        model = arrayOf(
-                GREEN, GREEN, GREEN, GREEN,
-                RED, RED, RED, RED,
-                BLUE, BLUE, BLUE, BLUE,
-                ORANGE, ORANGE, ORANGE, ORANGE,
-                WHITE, WHITE, WHITE, WHITE,
-                YELLOW, YELLOW, YELLOW, YELLOW
-        )
-    }
-
-    constructor(randomMoves: Int) {
-        val edgeModel = EdgeModel()
-        val r: Array<Int> = randomMoves(randomMoves)
-        val doMoves = edgeModel.doMoves(r)
-        this.model = doMoves.model
-    }
-
-    constructor(model: Array<Int>) {
-        this.model = model
-    }
-
-    constructor(moves: List<Int>) {
-        val edgeModel = EdgeModel()
-        val newModel = edgeModel.doMoves(moves)
-        this.model = newModel.model
-    }
 
     /**
      * Do a single move and calculate the resulting edge model.
@@ -125,7 +91,6 @@ class EdgeModel {
             copyOf[s[5]] = model[s[7]]
             copyOf[s[7]] = model[s[5]]
         }
-
         when (move) {
             F -> nonPrime(F_indices)
             F_ -> prime(F_indices)
@@ -146,7 +111,7 @@ class EdgeModel {
             D_ -> prime(D_indices)
             D2 -> double(D_indices)
         }
-        return EdgeModel(copyOf)
+        return EdgeModel.withModel(copyOf)
     }
 
     /**
@@ -171,14 +136,6 @@ class EdgeModel {
         return trimMargin
     }
 
-    fun doMoves(f: Array<Int>) : EdgeModel {
-        var edgeModel = this
-        f.forEach {
-            edgeModel = edgeModel.doMove(it)
-        }
-        return edgeModel
-    }
-
     fun doMoves(f: Collection<Int>): EdgeModel {
         var edgeModel = this
         f.forEach {
@@ -187,8 +144,12 @@ class EdgeModel {
         return edgeModel
     }
 
-    fun doMoves(vararg f: Int): EdgeModel {
-        return this.doMoves(f.toList())
+    fun doMoves(f: IntArray): EdgeModel {
+        var edgeModel = this
+        f.forEach {
+            edgeModel = edgeModel.doMove(it)
+        }
+        return edgeModel
     }
 
     /**
@@ -225,5 +186,62 @@ class EdgeModel {
             }
         }
     }
+
+    companion object {
+
+        private val F_indices = intArrayOf(13, 18, 7, 20, 3, 0, 1, 2)
+        private val B_indices = intArrayOf(8, 9, 10, 11, 16, 15, 22, 5)
+        private val L_indices = intArrayOf(3, 23, 9, 19, 12, 13, 14, 15)
+        private val U_indices = intArrayOf(16, 17, 18, 19, 0, 12, 8, 4)
+        private val D_indices = intArrayOf(2, 6, 10, 14, 20, 21, 22, 23)
+        private val R_indices = intArrayOf(4, 5, 6, 7, 1, 17, 11, 21)
+
+        fun solved(): EdgeModel {
+            val edgeModel = EdgeModel()
+            // do a sanity check
+            val entries = mutableListOf(F_indices, B_indices, L_indices, U_indices, D_indices, R_indices).flatMap { it.asList() }.groupBy { it }.entries
+//        println("entries = ${entries}")
+            if (entries.any {
+                        it.value.size != 2
+                    }) {
+                throw RuntimeException("each index should occur exactly twice in the arrays")
+            }
+
+            val model = intArrayOf(
+                    GREEN, GREEN, GREEN, GREEN,
+                    RED, RED, RED, RED,
+                    BLUE, BLUE, BLUE, BLUE,
+                    ORANGE, ORANGE, ORANGE, ORANGE,
+                    WHITE, WHITE, WHITE, WHITE,
+                    YELLOW, YELLOW, YELLOW, YELLOW
+            )
+            edgeModel.model = model
+            return edgeModel
+        }
+
+        fun withRandomMoves(randomMoves: Int): EdgeModel {
+            val edgeModel = EdgeModel()
+            val r: IntArray = randomMoves(randomMoves)
+            val doMoves = edgeModel.doMoves(r.toList())
+            edgeModel.model = doMoves.model
+            return edgeModel
+        }
+
+        fun withModel(model: IntArray): EdgeModel {
+            val edgeModel = EdgeModel()
+            edgeModel.model = model
+            return edgeModel
+        }
+
+        /**
+         * Pass a list of moves and do them on a solved edgemodel.
+         */
+        fun withMoves(moves: IntArray): EdgeModel {
+            val edgeModel = EdgeModel.solved()
+            val newModel = edgeModel.doMoves(moves)
+            edgeModel.model = newModel.model
+            return edgeModel
+        }
+    }
 }
 

src/main/kotlin/be/nielandt/EdgeModelFactoryIterator.kt

@@ -0,0 +1,66 @@
+package be.nielandt
+
+/**
+ * This thing helps us to create edgemodels using a counter. The advantage is that the edgemodel doesn't need to be calculated
+ * completely from scratch: previous states are kept, so if, e.g., the third digit changes in the counter (of length 5),
+ * the previous state that was calculated using the first two states is used to perform move 3,4,5 on.
+ *
+ * This is probably equivalent to 8 nested for loops, you'd be able to keep track of temporary solutions there too....
+ */
+class EdgeModelFactoryIterator(val original: EdgeModel, val counter: Iterator<IntArray>) {
+    // keep a modified version of the edgemodel for each digit in the counter, from left to right
+    private val history: MutableList<EdgeModel> = mutableListOf()
+    private var previous:IntArray
+    private var lastMoves: IntArray
+
+    init {
+        // init the history
+        val firstOne = counter.next()
+        lastMoves = firstOne
+        this.history.add(original.doMove(firstOne[0]))
+        for (i in 1 until firstOne.size) {
+            this.history.add(this.history.last().doMove(firstOne[i]))
+        }
+        // keep track of the 'previous move that was performed'
+        previous = firstOne
+    }
+
+    fun hasNext(): Boolean {
+        return counter.hasNext()
+    }
+
+    fun movesOfCurrent() : IntArray {
+        return previous
+    }
+
+    fun getNext(): EdgeModel {
+        // the next set of moves
+        val moves = counter.next()
+        this.lastMoves = moves
+        // figure out the first index that differs
+        val lastModifiedIndex = firstDifferingIndex(previous, moves)
+        // we only need to redo everything starting from the lastoverflowindex
+        // these are our moves, but we can salvage everything up to lastoverflowindex
+        // we have a history to work with... only redo what's necessary
+        for (i in lastModifiedIndex until moves.size) {
+            var start: EdgeModel = if (i == 0)
+                original
+            else
+                history[i - 1]
+            history[i] = start.doMove(moves[i])
+        }
+        // bump the previous value
+        previous = moves
+        // the last item in the history is now the edgemodel we need to test...
+        return history.last()
+    }
+
+    private fun firstDifferingIndex(previous: IntArray, moves: IntArray): Int {
+        previous.forEachIndexed { index, i ->
+            if(previous[index] != moves[index])
+                return index
+        }
+        // nothing changed.. that's probably impossible
+        throw IllegalStateException()
+    }
+}

src/main/kotlin/be/nielandt/Move.kt

@@ -26,7 +26,7 @@ const val L2 = 16
 const val R2 = 17
 
 fun decodeMove(i: Int): String {
-    return when(i) {
+    return when (i) {
         F -> "F"
         B -> "B"
         U -> "U"
@@ -48,18 +48,18 @@ fun decodeMove(i: Int): String {
         L2 -> "L2"
         R2 -> "R2"
         else -> {
-            println("i = ${i}")
+            println("i = $i")
             throw IllegalArgumentException()
         }
     }
 }
 
 fun classOf(move: Int): Int {
-    return (move%6) / 2
+    return (move % 6) / 2
 }
 
-fun parseMoves(s: String): List<Int> {
-    return s.split(" ", ",", ";").filter { it?.length > 0 }.map { parseMove(it) }.toList()
+fun parseMoves(s: String): IntArray {
+    return s.split(" ", ",", ";").filter { it?.length > 0 }.map { parseMove(it) }.toIntArray()
 }
 
 fun parseMove(s: String): Int {
@@ -91,10 +91,46 @@ fun parseMove(s: String): Int {
     }
 }
 
-fun randomMoves(amount: Int): Array<Int> {
+/**
+ * Get a proper scramble set of moves. Disallow the obvious symmetries.
+ */
+fun randomMoves(amount: Int): IntArray {
     val rgen = Random()
-    return Array(amount) {
-        rgen.nextInt(18)
+    val result = IntArray(amount)
+    for (i in 0 until result.size) {
+        // create valid options for the next one
+        val options = mutableListOf<Int>()
+        if (i == 0) {
+            // all options
+            options.addAll(0..17)
         }
+        // if there's two before us, we can't add a third of the same class
+        else if (i > 1 && classOf(result[i - 1]) == classOf(result[i - 2])) {
+            options.addAll(
+                    (0..17).filter { classOf(it) != classOf(result[i - 1]) }
+            )
+        } else {
+            // all options except the previous one
+            // also disallow same-face solutions
+            options.addAll(
+                    (0..17)
+                            // can't be the same face move
+                            .filter {
+                                it % 6 != result[i - 1] % 6
+                            }
+            )
+        }
+        result[i] = options[rgen.nextInt(options.size)]
+    }
+    return result
 }
 
+fun main(args: Array<String>) {
+    printMoves(randomMoves(50))
+}
+
+fun printMoves(moves: IntArray) {
+    println(moves.map { decodeMove(it) }.joinToString(","))
+}
+
+

src/main/kotlin/be/nielandt/counter/Counter.kt

@@ -12,7 +12,7 @@ open abstract class Counter(size: Int, val base: Int = 18) {
     /**
      * Empty counter, all 0 values for each digit.
      */
-    var counter: Array<Int> = Array(size) { 0 }
+    var counter: IntArray = IntArray(size) { 0 }
 
     /**
      *  The last (highest significance) index that overflowed and has been changed in the counter. Could be null, if it never overflowed.

src/main/kotlin/be/nielandt/counter/CounterBasic.kt

@@ -61,3 +61,12 @@ class CounterBasic(size: Int) : Counter(size, 18) {
     }
 
 }
+
+fun main(args: Array<String>) {
+    val counterBasic = CounterBasic(7)
+    var count = 0
+    while(counterBasic.increase())
+        count++
+    println("count = ${count}")
+
+}

src/main/kotlin/be/nielandt/counter/CounterBuffer.kt

@@ -7,14 +7,14 @@ import be.nielandt.classOf
  */
 class CounterBuffer(size: Int) : Counter(size, 18) {
 
-    val buffer = mutableListOf<Array<Int>>()
+    val buffer = mutableListOf<IntArray>()
 
     init {
         // initialise the buffer of valid counters
         val counterBasic = CounterBasic(size)
         do {
             if (counterBasic.isValid()) {
-                buffer.add(counterBasic.counter)
+                buffer.add(counterBasic.counter.copyOf())
             }
         } while (counterBasic.increase())
         println("Init of counter buffer, ${buffer.size} valid combos")

src/main/kotlin/be/nielandt/counter/CounterTiered.kt

@@ -7,9 +7,9 @@ import be.nielandt.decodeMove
  * 1) tier1 : axes / move classes (FB/UD/RL) -> three classes, but multiple sizes (1 or 2) possible
  * 2) tier2: each block of class (22, 11, 2, 11, 0, ...) needs to be expanded into the full range of related moves
  */
-class CounterTiered : Counter {
+class CounterTiered : Counter(8) {
 
-    private val moveIterator: Iterator<Array<Int>>
+    private val moveIterator: Iterator<IntArray> = listOf<IntArray>().iterator()
 
     override fun increase(): Boolean {
         if (!this.moveIterator.hasNext())
@@ -18,20 +18,14 @@ class CounterTiered : Counter {
         return true
     }
 
-
-    constructor(size: Int) : super(size, 18) {
-        this.moveIterator = moveIterator().iterator()
-        this.increase()
-    }
-
     override fun atMax(): Boolean {
         return !this.moveIterator.hasNext()
     }
 
-    private class MoveIterator(val classes: List<List<Int>>) : Iterator<Array<Int>> {
+    private class MoveIterator(val classes: List<IntArray>) : Iterator<IntArray> {
 
         var currentClassIndex = 0
-        lateinit var currentMoves: Iterator<Array<Int>>
+        lateinit var currentMoves: Iterator<IntArray>
 
 
         init {
@@ -40,11 +34,11 @@ class CounterTiered : Counter {
         }
 
         private fun doClass(index: Int) {
-            val fillIn = fillIn(0, classes[index], Array(classes.size) { 0 })
+            val fillIn = fillIn(0, classes[index], IntArray(classes.size) { 0 })
             currentMoves = fillIn.toList().iterator()
         }
 
-        override fun next(): Array<Int> {
+        override fun next(): IntArray {
             val next = currentMoves.next()
             if (!currentMoves.hasNext()) {
                 nextClass()
@@ -65,73 +59,17 @@ class CounterTiered : Counter {
 
     }
 
-    fun moveIterator(): Iterator<Array<Int>> {
-        return MoveIterator(classIterator()).iterator()
-    }
 
-    /**
-     * These are the classes (FB/UD/RL), correctly configured (no illegal combinations here)
-     */
-    fun classIterator(): List<List<Int>> {
-        val classes = appendRandomClass(this.counter.size, listOf())
-        return classes
-    }
-
-    /**
-     * Helper function for classIterator()
-     */
-    private fun appendRandomClass(size: Int, base: List<Int>): List<List<Int>> {
-        val result = mutableListOf<List<Int>>()
-        when {
-            base.size < size - 1 -> // add all classes, but don't repeat a group already there
-                (0..2).filter { if (base.isNotEmpty()) it != base.last() else true }
-                        .forEach { theClass ->
-                            // and both amounts, 1+2
-                            (1..2).forEach { amount ->
-                                val l = base.toMutableList()
-                                for (i in 1..amount) {
-                                    l.add(theClass)
-                                }
-                                result.addAll(appendRandomClass(size, l))
-                            }
-                        }
-            base.size == size -> {
-                // we're done here
-                result.add(base)
-            }
-            base.size == size - 1 -> // the base is not empty, only add class that is not at the end of the base list
-                (0..2).filter { if (base.isEmpty()) true else it != base.last() }.forEach { theClass ->
-                    val l = base.toMutableList()
-                    l.add(theClass)
-                    result.add(l)
-                }
-        }
-        return result
-    }
 }
 
 class CounterTieredFactory {
     companion object {
         fun create(size: Int): CounterTiered {
-            return CounterTiered(size)
+            return CounterTiered()
         }
     }
 }
 
-fun main(args: Array<String>) {
-    var count = 0
-    CounterTieredFactory.create(4).classIterator().forEach {
-        println("it = ${it}")
-        count++
-    }
-    println("count = ${count}")
-//    CounterTieredFactory.create(7).moveIterator().forEach {
-//        println("Arrays.tostring(it) = ${Arrays.toString(it)} ${it.map { decodeMove(it) }.toList()}")
-//        count++
-//    }
-//    println("count = ${count}")
-}
-
 /**
  * Expand the class ints into the full range of moves.
  *
@@ -159,8 +97,8 @@ const val D2 = 15
 const val L2 = 16
 const val R2 = 17
  */
-fun fillIn(index: Int, classes: List<Int>, moveList: Array<Int>): List<Array<Int>> {
-    val result = mutableListOf<Array<Int>>()
+fun fillIn(index: Int, classes: IntArray, moveList: IntArray): List<IntArray> {
+    val result = mutableListOf<IntArray>()
 
     // if the movelist is complete, finish it
     if (index == classes.size) {

src/main/kotlin/be/nielandt/counter/VariableCounter.kt

@@ -0,0 +1,55 @@
+package be.nielandt.counter
+
+import java.util.*
+
+/**
+ * The variable counter has irregular base size for each digit.
+ *
+ * basesize: [1,3,2]
+ * iterates:
+ * - [0,0,0]
+ * - [0,0,1]
+ * - [0,1,0]
+ * - [0,1,1]
+ * - [0,2,0]
+ * - [0,2,1]
+ */
+class VariableCounter(internal val baseSizes: IntArray) : Iterator<IntArray> {
+
+    // init the counter with 0's, we only have a maximum as our basesize
+    val counter = IntArray(baseSizes.size) {
+        when (it) {
+            baseSizes.size - 1 -> -1
+            else -> 0
+        }
+    }
+
+    override fun hasNext(): Boolean {
+        // check if all elements in the counter has reached their maximum (basesize - 1)
+        counter.forEachIndexed { index, sh ->
+            if (sh < baseSizes[index] - 1)
+                return true
+        }
+        return false
+    }
+
+    override fun next(): IntArray {
+        for (i in this.counter.size - 1 downTo 0) {
+            this.counter[i]++
+            if (this.counter[i] == baseSizes[i]) {
+                this.counter[i] = 0
+            } else {
+                break
+            }
+        }
+        return counter.copyOf()
+    }
+}
+
+fun main(args: Array<String>) {
+    val counter = VariableCounter(intArrayOf(2, 3, 2))
+    while (counter.hasNext()) {
+        val next = counter.next()
+        println("counter.next() = ${Arrays.toString(next)} ${counter.hasNext()}")
+    }
+}

src/main/kotlin/be/nielandt/iterator/ValidClassMoveIterator.kt

@@ -0,0 +1,55 @@
+package be.nielandt.iterator
+
+class ValidClassMoveIterator(val size: Int) : Iterator<IntArray> {
+
+    // current level of the iterator
+    var classesIterator = ValidClassesIterator(size)
+    var movesIterator: ValidMoveIterator
+
+    init {
+        this.movesIterator = ValidMoveIterator(classesIterator.next())
+    }
+
+    override fun hasNext(): Boolean {
+        // check if we have another move in the move iterator
+        return if (this.movesIterator.hasNext()) {
+            true
+        } else {
+            // the moves iterator does not has any more juice, move to the next class
+            if (!this.classesIterator.hasNext()) {
+                false
+            } else {
+                nextClass()
+                this.movesIterator.hasNext()
+            }
+        }
+    }
+
+    override fun next(): IntArray {
+        // check if there's a valid move left
+        if (!this.movesIterator.hasNext()) {
+            nextClass()
+        }
+        // now we're sure there's something left
+        return this.movesIterator.next()
+    }
+
+    /**
+     * Bump the 'current class'. This means we have a new moves iterator at our disposal.
+     */
+    private fun nextClass() {
+        val next = this.classesIterator.next()
+        this.movesIterator = ValidMoveIterator(next)
+    }
+}
+
+fun main(args: Array<String>) {
+    val validClassMoveIterator = ValidClassMoveIterator(8)
+    var count=0
+    while (validClassMoveIterator.hasNext()) {
+        validClassMoveIterator.next()
+//        println("Arrays.toString(validClassMoveIterator.next()) = ${validClassMoveIterator.next().map { decodeMove(it) }}")
+        count++
+    }
+    println("count = ${count}")
+}

src/main/kotlin/be/nielandt/iterator/ValidClassesIterator.kt

@@ -0,0 +1,70 @@
+package be.nielandt.iterator
+
+import java.time.Duration
+import java.time.Instant
+
+class ValidClassesIterator(val size: Int) : Iterator<List<Int>> {
+
+    private var classes: Iterator<List<Int>> = classIterator().iterator()
+
+    override fun hasNext(): Boolean {
+        return this.classes.hasNext()
+    }
+
+    override fun next(): List<Int> {
+        return this.classes.next()
+    }
+
+    /**
+     * These are the classes (FB/UD/RL), correctly configured (no illegal combinations here)
+     */
+    private fun classIterator(): List<List<Int>> {
+        val classes = appendRandomClass(size, listOf())
+        return classes
+    }
+
+    /**
+     * Helper function for classIterator()
+     */
+    private fun appendRandomClass(size: Int, base: List<Int>): List<List<Int>> {
+        val result = mutableListOf<List<Int>>()
+        when {
+            base.size < size - 1 -> // add all classes, but don't repeat a group already there
+                (0..2).filter { if (base.isNotEmpty()) it != base.last() else true }
+                        .forEach { theClass ->
+                            // and both amounts, 1+2
+                            (1..2).forEach { amount ->
+                                val l = base.toMutableList()
+                                for (i in 1..amount) {
+                                    l.add(theClass)
+                                }
+                                result.addAll(appendRandomClass(size, l))
+                            }
+                        }
+            base.size == size -> {
+                // we're done here
+                result.add(base)
+            }
+            base.size == size - 1 -> // the base is not empty, only add class that is not at the end of the base list
+                (0..2).filter { if (base.isEmpty()) true else it != base.last() }.forEach { theClass ->
+                    val l = base.toMutableList()
+                    l.add(theClass)
+                    result.add(l)
+                }
+        }
+        return result
+    }
+}
+
+fun main(args: Array<String>) {
+    val now = Instant.now()
+    val iter = ValidClassesIterator(8)
+    var count: Int = 0
+    while(iter.hasNext()) {
+        println("iter.next() = ${iter.next()}")
+        count++
+    }
+    println("count = ${count}")
+    println("Duration.between(Instant.now(), now) = ${Duration.between(now, Instant.now()).toMillis()}")
+}
+

src/main/kotlin/be/nielandt/iterator/ValidMoveIterator.kt

@@ -1,13 +1,82 @@
 package be.nielandt.iterator
 
-class ValidMoveIterator: Iterator<Array<Int>> {
+import be.nielandt.counter.VariableCounter
+import be.nielandt.decodeMove
+import java.util.*
 
-    override fun hasNext(): Boolean {
-        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+/**
+ * Iterates over the different moves of the given specific classes.
+ */
+class ValidMoveIterator(val classes: List<Int>) : Iterator<IntArray> {
+
+    internal var expansionCounter: VariableCounter
+
+    /**
+     * At initialisation time, create the internal expansion counter. This one will count appropriately for each class type,
+     * depending on whether the class is alone or is a duplicate.
+     */
+    init {
+        // create the variable counter: if a class is 'alone', it can iterate over all 6 values. otherwise, each part can iterate over 3
+        val intArray = IntArray(classes.size)
+        var i = 0
+        while (i < classes.size) {
+            if (i < classes.size - 1 && classes[i] == classes[i + 1]) {
+                intArray[i] = 3
+                intArray[i + 1] = 3
+                i += 2
+            } else {
+                intArray[i] = 6
+                i++
+            }
+        }
+        this.expansionCounter = VariableCounter(intArray)
     }
 
-    override fun next(): Array<Int> {
-        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
-    }
+    override fun hasNext(): Boolean = this.expansionCounter.hasNext()
 
+    override fun next(): IntArray {
+        val next = this.expansionCounter.next()
+        // translate this state into a list of moves
+        var i = 0
+        while (i < next.size) {
+            // process the double situation
+            if (i < classes.size-1 && classes[i] == classes[i + 1]) {
+                // so, we're in the same state, the first counter will get the 'low' value, the second the 'high' value
+                // for class FB, that would be F and B respectively
+                // class 0 (FB) has to expand to 0,6,12 (F,F_F2) and 1,7,13 (B,B_,B2) respectively
+                // class 1 (UD) has to expand to 2,8,14 (U,U_U2) and 3,9,15 (D,D_,D2) respectively
+                // class 2 (LR) has to expand to 4,10,16 (L,L_L2) and 5,11,17 (R,R_,R2) respectively
+                // next will contain 0,1,3, as the classes are a pair
+                val c1 = (classes[i] * 2) + 6 * next[i]
+                val c2 = (classes[i] * 2) + 6 * next[i + 1]+1
+                next[i] = c1
+                next[i + 1] = c2
+
+                // bump up the counter by two
+                i += 2
+            }
+            // now the single situation
+            else {
+                // class 0 (FB) has to expand to 0,1,6,7,12,13 (F,B,F_,B_,F2,B2)
+                // class 1 (UD) has to expand to 2,3,8,9,14,15 (U,D,U_,D_,U2,D2)
+                // class 2 (LR) has to expand to 4,5,10,11,16,17 (L,R,L_,R_,L2,R2)
+                next[i] = (classes[i] * 2) + ((next[i] / 2) * 6) + (next[i] % 2)
+                i++
+            }
+        }
+        return next
+    }
+}
+
+fun main(args: Array<String>) {
+    val validMoveIterator = ValidMoveIterator(listOf(0, 0, 2, 1, 2, 0, 1, 1))
+    println("classes = ${validMoveIterator.classes}")
+    println("basesizes = ${Arrays.toString(validMoveIterator.expansionCounter.baseSizes)}")
+    var count = 0
+    while (validMoveIterator.hasNext()) {
+        println("Arrays.toString(validMoveIterator.next()) = ${Arrays.toString(validMoveIterator.next())}")
+        println("validMoveIterator = ${validMoveIterator.next().map { decodeMove(it) }}")
+        count++
+    }
+    println("count = $count")
 }

src/test/kotlin/be/nielandt/EdgeModelTest.kt

@@ -7,7 +7,7 @@ class EdgeModelTest {
 
     @Test
     fun testSingleMove() {
-        val edgeModel = EdgeModel()
+        val edgeModel = EdgeModel.solved()
         (0..5).forEach { color ->
             assertTrue(edgeModel.crossSolved(color))
         }
@@ -15,7 +15,7 @@ class EdgeModelTest {
 
     @Test
     fun testSingleMoves() {
-        val edgeModel = EdgeModel()
+        val edgeModel = EdgeModel.solved()
         println(edgeModel)
         val final = edgeModel.doMove(F)
         println(final)