Data commit

Task/Determinant-and-permanent/Scala/determinant-and-permanent.scala

@@ -0,0 +1,25 @@
+def permutationsSgn[T]: List[T] => List[(Int,List[T])] = {
+  case Nil => List((1,Nil))
+  case xs => {
+    for {
+      (x, i) <- xs.zipWithIndex
+      (sgn,ys) <- permutationsSgn(xs.take(i) ++ xs.drop(1 + i))
+    } yield {
+      val sgni = sgn * (2 * (i%2) - 1)
+      (sgni, (x :: ys))
+    }
+  }
+}
+
+def det(m:List[List[Int]]) = {
+  val summands =
+    for {
+      (sgn,sigma) <- permutationsSgn((0 to m.length - 1).toList).toList
+    }
+    yield {
+      val factors =
+        for (i <- 0 to (m.length - 1))
+        yield m(i)(sigma(i))
+      factors.toList.foldLeft(sgn)({case (x,y) => x * y})
+    }
+  summands.toList.foldLeft(0)({case (x,y) => x + y})