Advent of Code 2023 Day 3

Section

schematic = """
467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..
"""

defmodule EngineSchematic do
  def parse(schematic) do
    schematic
    |> String.split("\n", trim: true)
    |> Enum.map(fn row -> String.split(row, "", trim: true) end)
  end

  def indexify(parsed_schematic) do
    parsed_schematic
    |> Enum.map(fn row -> Enum.with_index(row) end)
    |> Enum.with_index()
  end

  def process_acc(acc, number, index, row_index) do
    first = Enum.at(acc, 0)

    if first && first.end + 1 == index do
      List.replace_at(acc, 0, %{
        number: first.number <> number,
        start: first.start,
        end: index,
        row_index: row_index
      })
    else
      [%{number: number, start: index, end: index, row_index: row_index} | acc]
    end
  end

  def process_row(row, row_index) do
    row
    |> Enum.filter(fn {value, _index} -> Regex.match?(~r/\d/, value) end)
    |> Enum.reduce([], fn {number, index}, acc -> process_acc(acc, number, index, row_index) end)
  end

  def get_numbers(parsed_schematic) do
    indexify(parsed_schematic)
    |> Enum.map(fn {row, row_index} -> process_row(row, row_index) end)
    |> Enum.filter(fn row -> Enum.count(row) > 0 end)
    |> List.flatten()
  end

  def process_row_gears(row, row_index) do
    row
    |> Enum.filter(fn {value, _index} -> Regex.match?(~r/\*/, value) end)
    |> Enum.reduce([], fn {_number, index}, acc ->
      [%{index: index, row_index: row_index} | acc]
    end)
  end

  def get_gears(parsed_schematic) do
    indexify(parsed_schematic)
    |> Enum.map(fn {row, row_index} -> process_row_gears(row, row_index) end)
    |> Enum.filter(fn row -> Enum.count(row) > 0 end)
    |> List.flatten()
  end

  def assign_rects(number, parsed_schematic, rows, columns) do
    left = if number.start > 0, do: number.start - 1, else: number.start
    right = if number.end < columns - 1, do: number.end + 1, else: number.end
    top = if number.row_index > 0, do: number.row_index - 1, else: number.row_index
    bottom = if number.row_index < rows - 1, do: number.row_index + 1, else: number.row_index
    left_rect = [Enum.at(Enum.at(parsed_schematic, number.row_index), left)]
    right_rect = [Enum.at(Enum.at(parsed_schematic, number.row_index), right)]

    top_rect =
      if number.row_index > 0 do
        [Enum.slice(Enum.at(parsed_schematic, number.row_index - 1), left..right)]
      else
        []
      end

    bottom_rect =
      if number.row_index < rows - 1 do
        [Enum.slice(Enum.at(parsed_schematic, number.row_index + 1), left..right)]
      else
        []
      end

    Map.merge(number, %{
      left: left,
      right: right,
      top: top,
      bottom: bottom,
      rect: List.flatten(left_rect ++ right_rect ++ top_rect ++ bottom_rect)
    })
  end

  def process_numbers(numbers, parsed_schematic, rows, columns) do
    numbers
    |> Enum.map(fn number -> assign_rects(number, parsed_schematic, rows, columns) end)
    |> Enum.filter(fn number ->
      Enum.any?(number.rect, fn elem -> Regex.match?(~r/[^\d\.]/, elem) end)
    end)
  end

  def get_numbers_for_gear(numbers, gear) do
    Enum.filter(numbers, fn number ->
      gear.row_index in number.top..number.bottom &amp;&amp; gear.index in number.left..number.right
    end)
  end

  def go(schematic) do
    parsed_schematic = parse(schematic)

    parsed_schematic
    |> get_numbers
    |> process_numbers(
      parsed_schematic,
      Enum.count(parsed_schematic),
      Enum.count(Enum.at(parsed_schematic, 0))
    )
    |> Enum.map(fn el -> String.to_integer(el.number) end)
    |> Enum.sum()
  end

  def go2(schematic) do
    parsed_schematic = parse(schematic)
    gears = get_gears(parsed_schematic)

    numbers =
      parsed_schematic
      |> get_numbers
      |> process_numbers(
        parsed_schematic,
        Enum.count(parsed_schematic),
        Enum.count(Enum.at(parsed_schematic, 0))
      )

    gears
    |> Enum.map(fn gear -> Map.merge(gear, %{numbers: get_numbers_for_gear(numbers, gear)}) end)
    |> Enum.filter(fn gear -> Enum.count(gear.numbers) == 2 end)
    |> Enum.map(fn gear ->
      Enum.reduce(gear.numbers, 1, fn number, acc -> acc * String.to_integer(number.number) end)
    end)
    |> Enum.sum()
  end
end

parsed_schematic = EngineSchematic.parse(schematic)

numbers = EngineSchematic.go(schematic)

full_schematic = """
..........................................389.314.................206......................449.523..................138.....................
.........+.....954......723..........................................*.............687.....*..........692..........*........................
121......992...............*.......%585....814............936.......102..#353.........*.....140.........*..434..301..................%..315.
.../....................877................*...523............489.................*....380.......174..263.@..............824......710.......
...........$..733*758.......435...656...483.....................*..%855........154.779.....674...............320+....+........373...........
........707......................................503.422...591.551......676............306...*....................220..........@..410..639..
..................+....146.486.772..................*........*.....+848..*...863........-.....405........../..............636........*......
........190.....313.&.....*...../...+738..397.....@........#.840........167.../......#....508.......498..819..............*.........147.313.
....692*............177........................727..364..800.......................748..../........*...........%733......993.854........+...
...........*..............245..........128.............*.................322......................305....7*.......................152.......
........978.160..378.........*524.......*..905.343..+.681......615......-..........................................$..........@.............
.251..................................417.....*....53...........*...........354*126........119$...942....424....863...518*....971..96.48....
.................92.....441.681...532........................257.....932..............%...................*...............64.........*......
...........2.235*..........*..........*318.......317............................383.567..705.923..716.409.68.......................*........
...........*...................638..72...........+......367........802.........&..............=....*..*................-.../....401.773.....
........535...................*............4.29..........*.....784*....526........................141.342.189........630..958...............
...../.........745..+118....639....702.....%...#.*327...741............*......./324......531....................648/..............566.......
...+..172.........*.................................................910.....@.............*.....939................................*........
.799......37.307..140........334....@..204.852......+.....104............914..553..........994.&........547.#539........588$.......436......
.........*......*............*....12..../...&..914..223...$......+...........*....953+.......................................62........&....
........311.98.317...595..467................................#..142......*...620........$.......795.....363..135/..968...222.*....448...754.
...................../...............*702..881...............31.......630...............834........*.......-.........*.....*.527....*.......
..............614...........640+..888.......*....360........................%....764...............859.......586.....979.514.......30.......
.........@538........=...................176......*..200.300..............708...=......460...503..............*...............385...........
....................896.......$...................14....*..../........404..........-..*.......*.............688.460....$......&.............
......677...................110......&..-.....549..........934....654...-....334..153.508.....556......913........*....199........513.......
.........*....-...=204..342........515..85......./..955............../.......*..............-......18.*..........601..........+.......280...
.........80..515.........*.......$.........259...............250.../.......3..337.......%83..972..*....586.5.651......594....484............
..........................126.121......935*......235.815.......*.887........*........34..........294........*............$..............@...
45......$..651....$...............................*.........526.............41......*......302...................530..........@819.......463
.....710......*....26................734.......791......565............625.......%.887........@.......381..741..*...........................
......................881...........*............................989......+....235..............491...*...-.....693.........16..............
.............589*.....*.............610...318..#187..945@..774............................491.....*...867..................$...........679..
........957......614..553....345*56......#..................*...658.870........895......%........714......749...13..........................
...........$....................................127........775.....*......988..*.........254.276.................*..560.950.............*...
....761.................................825.........495..............496.....+.87.............*....*....689..26....*.....*...........131.745
639...*.196.....993*.......................*.603......*.............%................637....951.720........*......167...28..................
........./....-.....503........$.........634....*476...887.....463....221....457.........................698....................413.539*....
672..116...415................641....911...................774........*.......*.....................................926.674*693..&......103.
....*....%.....246.....................*...............290*.........59..542.253..$.....&......=.......320....196*...................586.....
...630..165....=...*.................690...360...........................*........42..584..650...153...*.........191........#218.....*......
.............*......51....680....102........*.......112...-....190......499.889&.................-...28....*........................340.....
...*729...130.683...........*....*.......776...928.....*..351....*...............878....................681.889...564*55................/760
839.................226...246...719..954.............428.........663.......341...+...357..................................../394............
......................*..............................................................*.....=910....821.........242......955......*569.......
......964.381.........923.....................491..906.....614........937....471..491....*........*....512....$...............574...........
........+..+.......................893..22.....*...........*............*.......@.........378......675./..........$103......................
...............525......$..=35....+.....*...301.......162.872......910.889.354............................871.679......894......731.........
...178........*.......543............865................*.....*857...........................630...........*....*.....@........&............
....#........954...............................433&..615...828............................*.....*745...+...556..321..................342....
..........................422...+..130.154.........................+..............225..235.501.........189..............609...............91
.....%........192....264.....$.609....*.....6..........932=.....*...920...........+...............391..............934.....*..211...=.......
.....805........*.......*975................$....159.........713....................&.850..$924.....-.....%..........*..212...*....176......
.............&..381..........917.905................*...276.............352...524.878..-........#......867....769.152........484.......341..
..664..390..140.......&.......*.........566.........163...*.&....995.....*...*..................811..............................874*.......
....=....$............43......989..............239......917..131.......13.....806....................................................174....
...........184..72.................=......928.....................684.....118.............239.........................#.....$...............
.609...116...*..*..........241...826.......*.......312......779=.....*...*......871.475...*...883.......717..538....-.581....424......259...
...*....*...33..574......&..%..................647*................378....803...*....#..260..*......543.-.......+.76..............464...*...
...611...42..............40...............375..........30......371............666...........185.....*.................161&........*.....968.
....................295.........-............-..................+......................*............789.........548................993......
..616....5.........*..........662.760............*670......272...........951........501.248....317......752.............616..739............
..........#..113..192..............$....267...761..........*...192.............456..............*.......*..........572....#....*............
............%...........606.............*...........628*.........*.342*503.....*...........409.......310........................516....316..
......622...................181.........454.............491....738...........214....#.........*..........937.....764#.......+...............
.........*..391=.....836...%.......................183..............402.............825...*....921..843...*.............+..897......546.....
.......264..............-..................$471........................*...174$.921........276.......*...513.......598.691............*.....
................$.64.......439......445..........701.......377...491%.422...........591........658...426.....*689..*.........687...=...175..
..171....429.260.............+........#...513.......*.....*...............477*..........375..&............641.....108..............444......
.....#....*.....................779..........*......140.24....................22.........@..28..............................................
.......682.....348+.153.168@......%.451.627.236.............92.141.....393........669.....................75.......557...585...826......559.
......................*.............*............881.........*....*776...*.105......*...=....#....&........&.526..+............#........%...
....955.....410......566..760....760........586....*....*...560........548.......335...951...749...256.........*......313....$...888........
...*....45.................*...................*..798.199....................77........................280&...347.207.@.....495.............
.934....*...36....841......952......266*....997............840...$867.......*....179...........@...................*.....86.....759..33*....
.......576...........*..........953....................722....%.............22..*...............952......965&.....777.....*....*........371.
..795................987....490..*..............................904.....4.......598....................................635..328.............
...............=563........#....270..........*.............=.......*..........+...............453.689.............=...................992...
...+......752..........................790...608.......914..69.....250.....200....996..892....=...*................472...@.............#....
..710......../.......604.................*.......401..=.............................*.#...........622...742..............685....&...........
......284..#............*.......401...802..........*...............65......166....901.....$..196*............65*................369.........
............815..................*........925....529........262....*........*...........234......729..37+.......95.......401................
.704..499%..........775....%....475....................287........379.......597....=...............................527..*.......264$........
................728*.......766......619*.....#604........./.75....................834....*.................912....*.....715.................
.......981.556..........................389........888.......*...............734......862.378...412........*......................556*......
..........*........................213........68..........696...............*.....................*.........726..678...@...931........991...
.../........=..............349.......*.........*....477.%.........#...=....7..............313...27....896.........*...13....................
...61..386.357.....=......*.......471.........126..&....579.....772....828..........322..*...............#.....644................844.......
.......*.......&.159...263............457...........................................@...772.....$...803..........................*....$158..
....202.....133......................*.................................362..................841.322...*..........730...868.....116..........
..........-.......................221..................41.................*...........=......*.........508.............=............465.....
...*667...979.983......................905..../......-.....321$.......731.690..........190.999....=.........*759....................*...515.
905...........*...............58.........*..801.....199..........305.=...........168.............298......25......&...604..........434......
..........531.217..497-.......*.......744.........................*......791.......*.................633.........657....................952.
......241...&...............675.156................831.........800..859...$....484.894...294......@....................825.655..627.........
.....*.............................*.586......790..*...178......................................716...*.......618.808-........*....*794.....
....401..+.....708.897.....655...351.../.426...*...148.....................798..........594............827...............166..784...........
........754.........&.......*...............+.............14....93..87.....@............*....205...-....................*..........224......
............784............88....................18.977..............*...................726...*....56.....575.........139..........*.......
.652...........*......*304.....*574.714.397........*.......*920...376....*....................627..........*................208...504.609...
.........535.......280......330.......=.*...............257...........+...738..@...271..453.................55....971......*..........@.....
..185.....%...931......%762.............902.........837..............922......34........*....915*.................*....%....158.............
.............................107.............*92.......*770...991*...................130.........256...910.....550......783............675..
....993........../...........*.........516.......*87..............147......268............................*........492*................*....
............190...611.....450...$.......*.....828....840.......................514.........................24..361.....485.......*504...778.
...............................809.486.552.........&....$....................=....*....206......576..595..........*382......................
...288..................$625........*..............382........318...........869.344..............*...&.....=361...................298.......
..............171..=525.............912...593..........@407......=....%43....................193.................676....&160...../..........
.................#.......262..............*.....259&............................724......35.....*879...............*........................
...........327..........-..........%...247...................381...................*32.......................183..735...............171.....
............$....................178.............925..70....*...............235................363......................97.764.792..*.......
.250..................*471............#....975....$.....*..42...13*687.............934...181....*.....62....532..9............*.....678.....
....*.......714.53..........245.....598...*..........251.......................116*.....*........269...=................483...../.......%...
....387......*..........498*............519........=..........$.......................600....373..........746.497..........#.248.........512
...........42....647.............776.........9......601....560.....696....267..................%....102...........250............289.33*....
......................667....793*......=521../.....................+........*......#....81.............*996.........*.............*.....713.
...........92............#.........*..................708................799...736.369....*.................-...779................439......
......484...*....655.......555..471.707....-..441....*.....882$........$.........=.........797........374..196...*...................../....
......../...284.............*...........297../....378................660.......*.....694.......709...*............499.................300...
..931...........752.986.805...................................52.783........887.127.....*........*...221....................=....../........
...*.......105.&.........*....141........................186.............-...............134....408......*230../709..767.....446.413........
..619.......*.......444...903.*.......594............446*.......*.........151.........................108..............*...............876..
............204.490...........285..74*.....898..373..........243....269+......616.....242........682..................923..582.....508*.....
486...=.........%.............................*..*...........................*......#.*............*.807..........*.......*....429..........
.....28.&.............416......851..968.....29..327.782..............706.....529..269.379........939...*...#...902.243..703.................
796......890.........*.........*....&...............*.......*...........*...................136.......944..52................@........451...
......................40..123...222..........52...408....995.......#149..708....$722....770*....*492.............714...%......99........%...
.....759.............................138+...+................................................517.......$....874.-.......54..................
.....*........................................=.......-......61...129.........517+...............264..130...*.....16........................
......769..176.........663..198...44.102...983......753..486...-.....*874.796.........-..........-...........941..../....973...........#....
...........@....74.......=.*........*..........$895.......=.......*......../........235....282.......243.......................337......69..
....................$.....................704..................283.328..........................218.............744............&...%82......
...........#.........252.......984............799.210..153..............699.29..........99............................*....648..............
............687..320.....518......*.............*.*.....#...........2...&...*...........*..19.356*......313.994.467..984...+................
.......#40..........*.....#...@....473.......789................/...*.......902......987..........179......*.................382..519.......
......................*.......11...............................926..153.#.................725*................................*.....*.......
...358...527..345..746.978....................*.........................607..798..899.........86.........*478.......888....949..767..807....
.....*...*.......%..............743*715..723...56................81.........*....=........345.........802.......776*...............$........
....26.743..........&943.................................................971.................%....527.................*....%...........@....
........................................782...............665......................532.......................998...991.702.542....406.779...
"""

numbers = EngineSchematic.go(full_schematic)

numbers = EngineSchematic.go2(full_schematic)

test_schematic = """
467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..
"""

EngineSchematic.go2(test_schematic)