June 2018 Update

Task/Longest-increasing-subsequence/Scala/longest-increasing-subsequence-1.scala

@@ -1,25 +1,36 @@
 object LongestIncreasingSubsequence extends App {
-  def longest(l: Array[Int]) = l match {
-    case _ if l.length < 2 => Array(l)
-    case l =>
-      def increasing(done: Array[Int], remaining: Array[Int]): Array[Array[Int]] = remaining match {
-        case Array() => Array(done)
-        case Array(head, _*) =>
-          (if (head > done.last) increasing(done :+ head, remaining.tail) else Array()) ++
-          increasing(done, remaining.tail) // all increasing combinations
-      }
-      val all = (1 to l.length).flatMap(i => increasing(l take i takeRight 1, l.drop(i+1))).sortBy(-_.length)
-      all.takeWhile(_.length == all.head.length).toArray // longest from all increasing combinations
-  }
-
   val tests = Map(
-    "3,2,6,4,5,1" -> Array("2,4,5", "3,4,5"),
-    "0,8,4,12,2,10,6,14,1,9,5,13,3,11,7,15" -> Array("0,2,6,9,11,15", "0,2,6,9,13,15", "0,4,6,9,13,15", "0,4,6,9,11,15")
+    "3,2,6,4,5,1" -> Seq("2,4,5", "3,4,5"),
+    "0,8,4,12,2,10,6,14,1,9,5,13,3,11,7,15" ->
+      Seq("0,2,6,9,11,15", "0,2,6,9,13,15", "0,4,6,9,13,15", "0,4,6,9,11,15")
   )
-  def asInts(s: String): Array[Int] = s split "," map Integer.parseInt
-  assert(tests forall {case (given, expect) =>
-      val lis = longest(asInts(given))
-      println(s"$given has ${lis.size} longest increasing subsequences, e.g. "+lis.last.mkString(","))
-      expect contains lis.last.mkString(",")
+
+  def lis(l: Array[Int]): Seq[Array[Int]] =
+    if (l.length < 2) Seq(l)
+    else {
+      def increasing(done: Array[Int], remaining: Array[Int]): Seq[Array[Int]] =
+        if (remaining.isEmpty) Seq(done)
+        else
+          (if (remaining.head > done.last)
+            increasing(done :+ remaining.head, remaining.tail)
+          else Nil) ++ increasing(done, remaining.tail) // all increasing combinations
+
+      val all = (1 to l.length)
+        .flatMap(i => increasing(l take i takeRight 1, l.drop(i + 1)))
+        .sortBy(-_.length)
+      all.takeWhile(_.length == all.head.length) // longest of all increasing combinations
+    }
+
+  def asInts(s: String): Array[Int] = s split "," map (_.toInt)
+
+  assert(tests forall {
+    case (given, expect) =>
+      val allLongests: Seq[Array[Int]] = lis(asInts(given))
+      println(
+        s"$given has ${allLongests.length} longest increasing subsequences, e.g. ${
+          allLongests.last
+            .mkString(",")
+        }")
+      allLongests.forall(lis => expect.contains(lis.mkString(",")))
   })
 }