diff --git a/aoc/src/main/scala/aoc/y2017/Day10.scala b/aoc/src/main/scala/aoc/y2017/Day10.scala
index 4ba2766..af2b67d 100644
--- a/aoc/src/main/scala/aoc/y2017/Day10.scala
+++ b/aoc/src/main/scala/aoc/y2017/Day10.scala
@@ -22,13 +22,7 @@ object Day10 extends Day {
     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 = {
+  def knotHash(input: String): String = {
     val magic = List(17, 31, 73, 47, 23)
     val codes = input.map(_.toInt) ++ magic
     val shifts = List.fill(64)(codes).flatten
@@ -39,4 +33,14 @@ object Day10 extends Day {
     hexed.mkString
   }
 
+  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 = {
+    knotHash(input)
+  }
+
 }
diff --git a/aoc/src/main/scala/aoc/y2017/Day13.scala b/aoc/src/main/scala/aoc/y2017/Day13.scala
new file mode 100644
index 0000000..447635d
--- /dev/null
+++ b/aoc/src/main/scala/aoc/y2017/Day13.scala
@@ -0,0 +1,34 @@
+package aoc.y2017
+
+import aoc.Day
+
+object Day13 extends Day {
+
+  import fastparse._, SingleLineWhitespace._
+
+  def parseNumber[_: P]: P[Int] = P(CharIn("0-9").rep(1).!).map(_.toInt)
+  def parseScanner[_: P]: P[(Int, Int)] = P(parseNumber ~ ": " ~ parseNumber)
+  def parseScanners[_: P]: P[Map[Int, Int]] = P(parseScanner.rep(1, "\n")).map(Map(_: _*))
+
+  def scannerAtStart(time: Int, range: Int): Boolean = (time % (2 * (range - 1))) == 0
+
+  def scanners(input: String): Map[Int, Int] = parse(input, parseScanners(_)).get.value
+  def severity(scanners: Map[Int, Int], delay: Int): Int = scanners.collect {
+    case (index, range) if scannerAtStart(index + delay, range) => index * range
+  }.sum
+
+  override def part1(input: String): String = {
+    severity(scanners(input), delay = 0).toString
+  }
+
+  override def part2(input: String): String = {
+    val parsedScanners = scanners(input)
+    lazy val packetDelays: LazyList[Int] = LazyList.from(0)
+    lazy val tripSeverities = packetDelays.map(delay => (delay, severity(parsedScanners, delay)))
+    val avoidanceDelay = tripSeverities.indexWhere {
+      case (delay, severity) => severity == 0 && delay % (2 * (parsedScanners(0) - 1)) != 0
+    }
+    avoidanceDelay.toString
+  }
+
+}
diff --git a/aoc/src/main/scala/aoc/y2017/Day14.scala b/aoc/src/main/scala/aoc/y2017/Day14.scala
new file mode 100644
index 0000000..8d5c88a
--- /dev/null
+++ b/aoc/src/main/scala/aoc/y2017/Day14.scala
@@ -0,0 +1,51 @@
+package aoc.y2017
+
+import aoc.Day
+
+object Day14 extends Day {
+
+  def getRows(input: String): Seq[BigInt] = {
+    val keyStrings = (0 to 127).map(row => s"$input-$row")
+    val knotHashes = keyStrings.map(Day10.knotHash)
+    knotHashes.map(BigInt(_, 16))
+  }
+
+  override def part1(input: String): String = {
+    val bigInts = getRows(input)
+    val bits = bigInts.map(_.bitCount).sum
+    bits.toString
+  }
+
+  override def part2(input: String): String = {
+    val bigInts = getRows(input)
+    val disk = bigInts.toVector.map { bigInt =>
+      (0 to bigInt.bitLength).toVector.map(bigInt.testBit).padTo(128, false).take(128)
+    }
+    type GroupedDisk = Vector[Vector[Option[Int]]]
+    val numberBlocks: GroupedDisk = disk.zipWithIndex.map {
+      case (row, y) => row.zipWithIndex.map {
+        case (true, x) => Some(y * 128 + x)
+        case (false, _) => None
+      }
+    }
+    def simplifyGroups(disk: GroupedDisk): GroupedDisk = {
+      disk.zipWithIndex.map {
+        case (row, y) => row.zipWithIndex.map {
+          case (None, _) => None
+          case (Some(g), x) =>
+            val left = if(x > 0) disk(y)(x - 1) else None
+            val right = if(x < 127) disk(y)(x + 1) else None
+            val up = if(y > 0) disk(y - 1)(x) else None
+            val down = if(y < 127) disk(y + 1)(x) else None
+            Vector(Some(g), left, right, up, down).collect { case Some(v) => v }.minOption
+        }
+      }
+    }
+    lazy val defrags: LazyList[GroupedDisk] = numberBlocks #:: defrags.map(simplifyGroups)
+    val (simplest, _) = defrags.zipWithIndex.takeWhile {
+      case (thisPass, index) => index < 1 || defrags(index - 1) != thisPass
+    }.last
+    simplest.flatten.collect { case Some(g) => g }.groupBy(identity).size.toString
+  }
+
+}
diff --git a/aoc/src/main/scala/aoc/y2017/Day15.scala b/aoc/src/main/scala/aoc/y2017/Day15.scala
new file mode 100644
index 0000000..49a94f3
--- /dev/null
+++ b/aoc/src/main/scala/aoc/y2017/Day15.scala
@@ -0,0 +1,48 @@
+package aoc.y2017
+
+import aoc.Day
+
+import scala.annotation.tailrec
+
+object Day15 extends Day {
+
+  import fastparse._, NoWhitespace._
+
+  def parseNumber[_: P]: P[Int] = P(CharIn("0-9").rep(1).!).map(_.toInt)
+  def parseGenerator[_: P](name: String): P[Int] = P("Generator " ~ name ~ " starts with " ~ parseNumber)
+  def parseGenerators[_: P]: P[(Int, Int)] = P(parseGenerator("A") ~ "\n" ~ parseGenerator("B"))
+
+  @tailrec def step(number: Int, multiplier: Int, forceMultiple: Int = 1): Int = {
+    val product = number.toLong * multiplier.toLong
+    val remainder = (product % Int.MaxValue).toInt
+    if(remainder % forceMultiple != 0) step(remainder, multiplier, forceMultiple)
+    else remainder
+  }
+
+  @tailrec def go(genANum: Int, genBNum: Int, genAMult: Int, genBMult: Int, forceMultipleA: Int = 1, forceMultipleB: Int = 1, left: Int = 40_000_000, sum: Int = 0): Int = {
+    if(left < 0) sum
+    else {
+      val nextA = step(genANum, genAMult, forceMultipleA)
+      val nextB = step(genBNum, genBMult, forceMultipleB)
+      val nextLeft = left - 1
+      val nextSum = if(((nextA ^ nextB) & ((1 << 16) - 1)) == 0) sum + 1 else sum
+      go(nextA, nextB, genAMult, genBMult, forceMultipleA, forceMultipleB, nextLeft, nextSum)
+    }
+  }
+
+  def run(input: String, pairs: Int, forceMultiple: Boolean): Int = {
+    val genAMult = 16807
+    val genBMult = 48271
+    val (genAStart, genBStart) = parse(input, parseGenerators(_)).get.value
+    go(genAStart, genBStart, genAMult, genBMult, if(forceMultiple) 4 else 1, if(forceMultiple) 8 else 1, pairs)
+  }
+
+  override def part1(input: String): String = {
+    run(input, pairs = 40_000_000, forceMultiple = false).toString
+  }
+
+  override def part2(input: String): String = {
+    run(input, pairs = 5_000_000, forceMultiple = true).toString
+  }
+
+}
diff --git a/aoc/src/main/scala/aoc/y2017/package.scala b/aoc/src/main/scala/aoc/y2017/package.scala
index 4536417..fdaf43a 100644
--- a/aoc/src/main/scala/aoc/y2017/package.scala
+++ b/aoc/src/main/scala/aoc/y2017/package.scala
@@ -15,7 +15,10 @@ package object y2017 extends Year {
     "10" -> Day10,
     "11" -> Day11,
     "12" -> Day12,
-    "25" -> Day25
+    "13" -> Day13,
+    "14" -> Day14,
+    "15" -> Day15,
+    "25" -> Day25,
   )
 
 }