Merge pull request #4946 from Kaiepi/challenge-132

Add Ben Davies' Scala 3 solutions for challenge 132

2 files changed, 47 insertions, 0 deletions

diff --git a/challenge-132/ben-davies/scala/ch-1.scala b/challenge-132/ben-davies/scala/ch-1.scala
new file mode 100644
index 0000000000..47f0e9f3af
--- /dev/null
+++ b/challenge-132/ben-davies/scala/ch-1.scala
@@ -0,0 +1,13 @@
+import java.time.LocalDate
+import java.time.format.DateTimeFormatter
+import java.time.temporal.ChronoUnit
+
+@main def ch1(input: String) = {
+  val formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd")
+  val birthday  = LocalDate.parse(input, formatter)
+  val today     = LocalDate.of(2021, 9, 22)
+  val lifetime  = ChronoUnit.DAYS.between(birthday, today)
+  val before    = birthday.minus(lifetime, ChronoUnit.DAYS)
+  val after     = today.plus(lifetime, ChronoUnit.DAYS)
+  println(before.format(formatter) + ", " + after.format(formatter))
+}
diff --git a/challenge-132/ben-davies/scala/ch-2.scala b/challenge-132/ben-davies/scala/ch-2.scala
new file mode 100644
index 0000000000..25b4297f0d
--- /dev/null
+++ b/challenge-132/ben-davies/scala/ch-2.scala
@@ -0,0 +1,34 @@
+implicit class Relation(r: NonEmptyTuple) {
+  inline def but(i: Int) = r.take(i) ++ r.drop(i).drop(1)
+}
+
+extension [S <: NonEmptyTuple](ss: List[S])
+  def hashjoin[R <: NonEmptyTuple](rs: List[R])(si: Int, ri: Int)(using Ordering[Tuple.Elem[S, si.type]]) = {
+    // 1. For each tuple r in the build input R
+    //    1.1 Add r to the in-memory hash table
+    val init = Map.empty[Tuple.Elem[S, si.type] | Tuple.Elem[R, ri.type], List[R]].withDefaultValue(List.empty)
+    val hash = rs.foldRight(init) { (r, acc) => acc.updated(r(ri), r :: acc(r(ri))) }
+    // 2. Do a final scan of the probe input S and add the resulting join
+    //    tuples to the output relation
+    ss sortBy { _(si) } flatMap { s => hash(s(si)) map { s ++ _.but(ri) } }
+  }
+
+@main def ch2 = {
+  val playerAges = List(
+    (20, "Alex" ),
+    (28, "Joe"  ),
+    (38, "Mike" ),
+    (18, "Alex" ),
+    (25, "David"),
+    (18, "Simon"),
+  )
+  val playerNames = List(
+    ("Alex", "Stewart"),
+    ("Joe",  "Root"   ),
+    ("Mike", "Gatting"),
+    ("Joe",  "Blog"   ),
+    ("Alex", "Jones"  ),
+    ("Simon","Duane"  ),
+  );
+  for r <- playerAges.hashjoin(playerNames)(1, 0) do println(r.toList.mkString(" "))
+}