Day 10

aoc/src/main/scala/aoc/y2017/Day06.scala

@@ -12,16 +12,6 @@ object Day06 extends Day {
     go(as, Set.empty)
   }
 
-  def rotateLeft[A](list: List[A], i: Int): List[A] = {
-    val size = list.size
-    list.drop(i % size) ++ list.take(i % size)
-  }
-
-  def rotateRight[A](list: List[A], i: Int): List[A] = {
-    val size = list.size
-    list.drop(size - (i % size)) ++ list.take(size - (i % size))
-  }
-
   case class State(blocks: List[Int]) {
 
     def step: State = {

aoc/src/main/scala/aoc/y2017/Day10.scala

@@ -0,0 +1,42 @@
+package aoc.y2017
+
+import aoc.Day
+
+object Day10 extends Day {
+
+  def knot(ring: List[Int], by: Int, at: Int): List[Int] = {
+    val shifted = rotateLeft(ring, at)
+    val (sHead, sTail) = shifted.splitAt(by)
+    val spliced = sHead.reverse ++ sTail
+    rotateRight(spliced, at)
+  }
+
+  def runShifts(shifts: List[Int]): List[Int] = {
+    val ring = (0 to 255).toList
+    val (last, _) = shifts.zipWithIndex.foldLeft((ring, 0)) {
+      case ((cr, acc), (shift, jump)) =>
+        val k = knot(cr, shift, acc)
+        val i = acc + shift + jump
+        (k, i)
+    }
+    last
+  }
+
+  override def part1(input: String): String = {
+    val shifts = input.split(',').map(_.toInt).toList
+    val last = runShifts(shifts)
+    (last.head * last.tail.head).toString
+  }
+
+  override def part2(input: String): String = {
+    val magic = List(17, 31, 73, 47, 23)
+    val codes = input.map(_.toInt) ++ magic
+    val shifts = List.fill(64)(codes).flatten
+    val last = runShifts(shifts)
+    val hashGroups = last.grouped(16)
+    val xored = hashGroups.map(_.reduce(_ ^ _))
+    val hexed = xored.map(_.toHexString.reverse.padTo(2, '0').reverse.toString)
+    hexed.mkString
+  }
+
+}

aoc/src/main/scala/aoc/y2017/package.scala

@@ -14,7 +14,18 @@ package object y2017 extends Year {
     "7" -> Day07,
     "8" -> Day08,
     "9" -> Day09,
+    "10" -> Day10,
     "25" -> Day25
   )
 
+  def rotateLeft[A](list: List[A], i: Int): List[A] = {
+    val size = list.size
+    list.drop(i % size) ++ list.take(i % size)
+  }
+
+  def rotateRight[A](list: List[A], i: Int): List[A] = {
+    val size = list.size
+    list.drop(size - (i % size)) ++ list.take(size - (i % size))
+  }
+
 }