Day 5 finaLLY

aoc/src/main/scala/aoc/y2018/Day05.scala

@@ -0,0 +1,40 @@
+package aoc.y2018
+import aoc.Day
+
+object Day05 extends Day {
+
+  def pair(c1: Char, c2: Char): Boolean = {
+    val c1l = c1.isLower
+    val c2l = c2.isLower
+    (c1l && !c2l && c1 == c2.toLower) || (!c1l && c2l && c1.toLower == c2)
+  }
+
+  def simpleLength(s: String): Int = {
+    s.foldLeft("") {
+        case (stack, ne) => {
+          if (stack.isEmpty) {
+            ne +: stack
+          } else {
+            val peek = stack.head
+            if (pair(ne, peek)) {
+              stack.tail
+            } else {
+              ne +: stack
+            }
+          }
+        }
+      }
+      .length
+  }
+
+  override def part1(input: String): String = {
+    simpleLength(input).toString
+  }
+
+  override def part2(input: String): String = {
+    val allChars = input.map(_.toLower).distinct.sortBy(c => input.count(_ == c))
+    val mapped = allChars.par.map(c => simpleLength(input.filter(_.toLower != c)))
+    mapped.min.toString
+  }
+
+}

aoc/src/main/scala/aoc/y2018/package.scala

@@ -7,6 +7,7 @@ package object y2018 extends Year {
     "2" -> Day02,
     "3" -> Day03,
     "4" -> Day04,
+    "5" -> Day05
   )
 
 }