tasks a-s

Task/N-queens-problem/Scala/n-queens-problem.scala

@@ -0,0 +1,20 @@
+case class Pos(row: Int, column: Int) {
+  def sameRow(p: Pos) = row == p.row
+  def sameColumn(p: Pos) = column == p.column
+  def sameDiag(p: Pos) = (p.column - column).abs == (p.row - row).abs
+  def illegal(p: Pos) = sameRow(p) || sameColumn(p) || sameDiag(p)
+  def legal(p: Pos) = !illegal(p)
+}
+
+def rowSet(size: Int, row: Int) = Iterator.tabulate(size)(column => Pos(row, column))
+
+def expand(solutions: Iterator[List[Pos]], size: Int, row: Int) =
+  for {
+    solution <- solutions
+    pos <- rowSet(size, row)
+    if solution forall (_ legal pos)
+  } yield pos :: solution
+
+def seed(size: Int) = rowSet(size, 0) map (sol => List(sol))
+
+def solve(size: Int) = (1 until size).foldLeft(seed(size)) (expand(_, size, _))