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copied!<p>After Andreas comment I changed the <code>m: Array[Array[Char]]</code> into <code>m: List[List[Char]]</code> which prevents any unnecessary and unwanted changes to it. The final looping method is </p> <pre><code> def reduc(f: (Int, Int) => Int, accu: Int, l: Int, u: Int, m1: List[List[Char]]):Int = accu + (l until u).toArray.par.reduce(f(accu, _) + f(accu, _)) </code></pre> <p>and I had to pass m as an argument to each used function, so every one of them had its own instance of it. The whole code:</p> <pre><code> object SudokuSolver extends App{ // The board is represented by an Array of strings (Arrays of Chars), val source = scala.io.Source.fromFile("./puzzle") val lines = source.getLines.toList val m: List[List[Char]] = for ( str <- lines; line: List[Char] = str.toList ) yield line source.close() // For prInting m def printSud(m: List[List[Char]]) = { Console.println("") m map (println) } Console.println("\nINPUT:") printSud(m) def invalid(i:Int, x:Int, y:Int, n:Char,m1: List[List[Char]]): Boolean = i < 9 && (m1(y)(i) == n || m1(i)(x) == n || m1(y / 3 * 3 + i / 3)(x / 3 * 3 + i % 3) == n || invalid(i + 1, x, y, n, m1)) def reduc(f: (Int, Int) => Int, accu: Int, l: Int, u: Int, m1: List[List[Char]]): Int = accu + (l until u).toArray.par.reduce(f(accu, _) + f(accu, _)) def search(x: Int, y: Int, accu: Int, m1: List[List[Char]]): Int = Pair(x, y) match { case Pair(9, y) => search(0, y + 1, accu, m1) // next row case Pair(0, 9) => { printSud(m1); accu + 1 } // found a solution case Pair(x, y) => if (m1(y)(x) != '0') search(x + 1, y, accu, m1) // place is filled, we skip it. else // box is not filled, we try all n in {1,...,9} reduc((accu: Int, n: Int) => { if (invalid(0, x, y, (n + 48).asInstanceOf[Char], m1)) accu else { // n fits here val line = List(m1(y).patch(x, Seq((n + 48).asInstanceOf[Char]), 1)) val m2 = m1.patch(y, line, 1) val newaccu = search(x + 1, y, accu, m2); val m3 = m1.patch(y, m1(y).patch(x, Seq(0), 1), 1) newaccu } }, accu, 1, 10, m1) } Console.println("\n" + search(0, 0, 0, m) + " solution(s)") } </code></pre>

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