[day6] solution

src/main/scala/Day6.scala

+package aoc2020
+import aoc2020.lib._
+
+def day6(input: List[String]): String =
+  //countGroupAnswersAny(input).sum.toString
+  countGroupAnswersAll(input).sum.toString
+
+def countGroupAnswersAny(input: List[String]): LazyList[Int] =
+  input.split("").map(_.flatMap(_.toArray).toSet.size)
+
+def countGroupAnswersAll(input: List[String]): LazyList[Int] =
+  input.split("").map(lines => {
+    val answers = lines.map(_.toSet)
+    answers.headOption
+      .map(h => answers.tail.fold(h)(_ intersect _))
+      .map(_.size)
+      .getOrElse(0)
+  })

src/main/scala/Main.scala

@@ -7,5 +7,6 @@ package aoc2020
     case 3 => input(boolChar('#'))(day3)
     case 4 => input()(day4)
     case 5 => input()(day5)
+    case 6 => input()(day6)
   }
   println(out)