1. val C = io.Source.fromFile("input").getLines.toList
  3. def parseMask(m: String) = {
  4. val oneIndexes = m.zipWithIndex.filter(_._1 == '1').map(x => 35L - x._2).toList
  5. val xIndexes = m.zipWithIndex.filter(_._1 == 'X').map(x => 35L - x._2).toList
  6. (oneIndexes, xIndexes)
  7. }
  9. def flipBitAtIndex(cur: Long, mIndexBit: (Long, Long)): Long = {
  10. val (mIdx, bitFlip) = mIndexBit
  11. bitFlip match {
  12. case 1L ⇒ cur | (1L << mIdx)
  13. case 0L ⇒ cur & ~(1L << mIdx)
  14. }
  15. }
  17. def applyMaskOnXIndexes(mIndex: Long, xIndexes: List[Long], mask: Long): Long = {
  19. // Flip X Indexes into 1 and 0 according to mask
  20. xIndexes.zipWithIndex.map {
  21. case (v, idx) ⇒ v → ((mask & (1L << idx)) >> idx)
  22. }
  23. // Apply it now to mIndex
  24. .foldLeft(mIndex)(flipBitAtIndex)
  26. }
  28. def expandMemoryIndexes(oneIndexes: List[Long], xIndexes: List[Long], index: Long) = {
  29. // Turn on all oneIndexes.
  30. var maskedIndex = oneIndexes.map(idx ⇒ (idx, 1L)).foldLeft(index)(flipBitAtIndex)
  32. // Turn off all xIndexes
  33. maskedIndex = xIndexes.map(idx ⇒ (idx, 0L)).foldLeft(maskedIndex)(flipBitAtIndex)
  35. var expandedIndexes: List[Long] = Nil
  36. // We iterate on how many Xes we have. 5 X? 2^5 masks iterated
  37. for (mask ← 0 until 1 << xIndexes.length) {
  38. expandedIndexes = applyMaskOnXIndexes(maskedIndex, xIndexes, mask) :: expandedIndexes
  39. }
  41. expandedIndexes
  42. }
  44. var oneIndexes = List[Long]()
  45. var xIndexes = List[Long]()
  47. var memory = scala.collection.mutable.Map[Long, Long]()
  49. C.foreach { line =>
  51. line.split(" = ") match {
  53. case Array("mask", maskString) ⇒
  54. val (ones, exes) = parseMask(maskString)
  55. oneIndexes = ones
  56. xIndexes = exes
  58. case Array(memCmd, memValue) ⇒
  59. val index = memCmd.substring(4, memCmd.length - 1).toLong
  60. expandMemoryIndexes(oneIndexes, xIndexes, index).foreach { idx =>
  61. memory(idx) = memValue.toLong
  62. }
  64. }
  66. }
  68. println(memory.values.sum)

Day 14 2