Sudoku

scala/src/main/scala/ch39_back_tracking/Sudoku.scala

@@ -0,0 +1,116 @@
+package ch39_back_tracking
+
+import scala.util.control.Breaks._
+
+class Sudoku {
+
+  def resolve(grid: Array[Array[Int]]): Unit = {
+    printGrid(grid)
+    println("")
+    if (resolve(grid, 0, 0)) {
+      printGrid(grid)
+    } else {
+      println("no result")
+      printGrid(grid)
+    }
+  }
+
+  private[this] def resolve(grid: Array[Array[Int]], theRow: Int, theColumn: Int): Boolean = {
+    if (theRow == 8 && theColumn == 9) {
+      //find the result
+      return true
+    }
+
+    var row = theRow
+    var column = theColumn
+    if (theColumn == 9) {
+      //move to next line
+      column = 0
+      row += 1
+    }
+
+    if (grid(row)(column) != 0) {
+      //given number, resolve next one
+      return resolve(grid, row, column + 1)
+    }
+
+    //start the real resolve
+    for (num <- 1 to 9) {
+      if (isOk(grid, row, column, num)) {
+        grid(row)(column) = num
+        if (resolve(grid, row, column + 1)) {
+          return true
+        }
+      }
+    }
+
+    //do not find anything, reset given row and column
+    grid(row)(column) = 0
+    false
+  }
+
+  def isOk(grid: Array[Array[Int]], row: Int, column: Int, num: Int): Boolean = {
+    isRowOk(grid, row, num) && isColumnOk(grid, column, num) && isSmallBoxOk(grid, row, column, num)
+  }
+
+  def isRowOk(grid: Array[Array[Int]], row: Int, num: Int): Boolean = {
+    var isOk = true
+    breakable {
+      for (column <- Range(0, 9)) {
+        if (grid(row)(column) == num) {
+          isOk = false
+          break
+        }
+      }
+    }
+    isOk
+  }
+
+  def isColumnOk(grid: Array[Array[Int]], column: Int, num: Int): Boolean = {
+    var isOk = true
+    breakable {
+      for (row <- Range(0, 9)) {
+        if (grid(row)(column) == num) {
+          isOk = false
+          break
+        }
+      }
+    }
+    isOk
+  }
+
+  def isSmallBoxOk(grid: Array[Array[Int]], row: Int, column: Int, num: Int): Boolean = {
+    val rowOffSet = (row / 3) * 3
+    val columnOffSet = (column / 3) * 3
+    var isOk = true
+    breakable {
+      for (i <- Range(0, 3)) {
+        for (j <- Range(0, 3)) {
+          if (grid(i + rowOffSet)(j + columnOffSet) == num) {
+            isOk = false
+            break
+          }
+        }
+      }
+    }
+    isOk
+  }
+
+  def printGrid(grid: Array[Array[Int]]): Unit = {
+    for (i <- Range(0, 9)) {
+      if (i % 3 == 0) {
+        println("-------------------------")
+      }
+      for (j <- Range(0, 9)) {
+        if (j % 3 == 0) {
+          print("| ")
+        }
+        print(grid(i)(j) + " ")
+      }
+      println("| ")
+
+    }
+    println("-------------------------")
+  }
+
+}

scala/src/test/scala/ch39_back_tracking/SudokuTest.scala

@@ -0,0 +1,74 @@
+package ch39_back_tracking
+
+import org.scalatest.FlatSpec
+
+class SudokuTest extends FlatSpec {
+
+  behavior of "SudokuTest"
+
+  it should "resolve - 1" in {
+    val grid = Array(
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0)
+    )
+    val sudoku = new Sudoku()
+    sudoku.resolve(grid)
+  }
+
+  it should "resolve - 2" in {
+    val grid = Array(
+      Array(0, 0, 7, 2, 5, 6, 4, 0 ,0),
+      Array(4, 0, 0, 0, 0, 0, 0, 0, 5),
+      Array(0, 1, 0, 0, 3, 9, 0, 6, 0),
+      Array(0, 0, 0, 5, 0, 8, 0, 0, 0),
+      Array(0, 0, 8, 0, 6, 0, 2, 0, 0),
+      Array(0, 9, 0, 1, 0, 7, 0, 0, 0),
+      Array(0, 3, 0, 0, 7, 0, 0, 9, 0),
+      Array(2, 0, 0, 0, 0, 0, 0, 0, 4),
+      Array(0, 0, 6, 3, 1, 2, 7, 0, 8)
+    )
+    val sudoku = new Sudoku()
+    sudoku.resolve(grid)
+  }
+
+  it should "resolve - 3" in {
+    val grid = Array(
+      Array(3, 8, 0, 0, 0, 0, 0, 0, 1),
+      Array(0, 0, 6, 4, 0, 0, 7, 8, 5),
+      Array(0, 0, 9, 0, 2, 0, 3, 0, 0),
+      Array(0, 6, 0, 0, 9, 0, 0, 0, 0),
+      Array(8, 0, 0, 3, 0, 2, 0, 0, 9),
+      Array(0, 0, 0, 0, 4, 0, 0, 7, 0),
+      Array(0, 0, 1, 0, 7, 0, 5, 0, 0),
+      Array(4, 9, 5, 0, 0, 6, 1, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 9, 2)
+    )
+    val sudoku = new Sudoku()
+    sudoku.resolve(grid)
+  }
+
+  it should "print grid" in {
+    val grid = Array(
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0),
+      Array(0, 0, 0, 0, 0, 0, 0, 0, 0)
+    )
+
+    val sudoku = new Sudoku()
+    sudoku.printGrid(grid)
+  }
+
+}