<!-- livebook:{"persist_outputs":true} -->
# Advent of Code 2023 - Day 3
## Sample
```elixir
sample = """
467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..
"""
```
<!-- livebook:{"output":true} -->
```
"467..114..\n...*......\n..35..633.\n......#...\n617*......\n.....+.58.\n..592.....\n......755.\n...$.*....\n.664.598..\n"
```
## Input
```elixir
input = """
...733.......289..262.....520..................161.462..........450.........................183.............................................
....*....................*.............707.352....*............/.....................801...@...............333..196........484.635......287.
....42.........131....913..............*......&..........634..................440..&...............83.....@...........404$..=....*..423.*...
618.......272....*.........&......547.344...............#............689.589.*....150......382=................................168......433.
..........=...............253.102*.........#......78.......804..........*........................858.........................-..............
...69.......*37...510.797...........596.946........#..................................602.175...............203..100..........681.......546.
...*.....110.....*......*..........*..........396......858=.......381....................*.......246*637..........=..391+...................
...973........274..551.............576.21@.......$..................*.......................................176............181.883......*...
.......223............+............................649.701.936...17..482..........80...........210.......+...=.........563.......*...222....
.373..*..................532....707.......956....@..+.....*......*...........+927.*......698......+....763.........275*.....27..498.........
....*......................+......*.........*..719....540.........24...=...........39...*...................514.........126..#..............
.....974.......952*308..@..........965....450............*4.343......772../..............437............=....*............./.....309........
............58..........840.....34................877........$............189..................*186......657.670................&.......854.
....22.406..*......883............*......880...........939...................................58.....387..................*..................
......*....587.........564/......599.......*...........*......................831.891/...552..........$.534+.....%802.975.960.346*..........
.792+..............828................-807.6...........326....324...722...334..*...........*................................................
.....................*.......................895..764*.........=...*........*..611..........79.......461@..546*940...818.346..........247...
....%....473......................288.......*....................932.....590...........918......791..................................*......
.....621...*........................*....129....425.10.....*.....................419....*.........*...166......#11...................831....
119........302.832.............159.506................*.229.....493....39...............587....523.......*..........610...805.559...........
......971.......*..........229*..........961........139..................+....411..................554....26.90.....$........*....-.........
...........463.615...................315....#...................................-...422.......109.-............*247................231.56...
..279*159.*...........126...569...............906..20..........990..........27.........%.......*.............................960-......./...
...........364....812*.......*..$.........812*....*.....369....&......176......................15.346#...#.....908...828..........-650......
.842*771....................189..9...............42...............897*...............479.................99.....+.......*...................
................842*356.849...............336.......201................412......./...@...........205....................956....*319.383*....
...438....&................*......../.......*.../...*....&.......62...*........348..............*....................54.....302.........298.
......$..318................264.....28...259..824..306...249.......&.392...444............889#..418....945...496..../.......................
................610.160......................................................%.699...987......................*.............................
..........@125.....*..............292..#....514..........................165....*...*....&.....*672.....551.194.426......53...500.599...278.
.275.192.........................*....854..#..............190............$.....40..662.706..774.........$................../..*......*......
....*.........*840....*638.....82...................520...*................................................../.190...719.......34....620....
...........532.....521................................*...423..75..........+....-........#...29.......258.605.....*..-......................
...........................37........../354.%453.....248.........*...561.481....727....437........969...*......243..........................
..................................183.........................+..250...+...................312.....=....150............@...229..............
...624...454*710..../..........=..*......../........%30....308..............................*................+...381..941........461.341....
......=............19.........297.......213..........................%............*522......442............962...-............92..-.....*...
.................................................324.663............775...290=.301...............=...15........=....780..................562
747........................438...35...806*.......*......................................%396..508......*700...16..-..$..230....443..617.....
.......$.........447......*...............336..424.........618........-..276......260............................452......#......*...*......
....824..@916....%...488..145....%.....55..........821.....#.....620.773....*116..*.......384............156.972................974..872....
...................=...........494.....*......609................*...............768..195..*......108/..........*......440..................
...187...........135.=.....44.........860..........$.......+..923...........966..........#..136.................423.......#....185..........
.....*....298........761.........................217....157..................*.....................292....268........#........./............
..789........../.375.........919.......425.........................542.....691..69..........184......*.......*.....578............531.......
.......740..619..*..............=........%....788.....+..324..........*..........*......531..*..=82....962.409.690..........981.............
......*...........652..+.........................*....32.#...........53...........761...*...353.....43*.......................*....6....611.
....589......../........190.362@....961...........917......*...........................165...............&..718...............633...*.......
.............781...565...............*................&..324...............................339..........964..+..........%..........427..312.
.........927.......*........#260......919.......828..469........585..........803............/...&.......................365.................
....406..........190........................308.*.................*.............*2.803&.........417....=............................955..126
.....#...61.75.......149....293.768....678#......675............449.....@...............%...............347......301.....-.490.....*........
............*........*.........*.............751........................888..&..348..49.747.........................*.318..#....888.........
..........160......335.................455....*.......761...................564..*............*926...654...../....907................857....
.....446.....................@....915.....&....639...=...........285..............567......862................731..............9........*...
..........513.............694..........$...............233..721.&................................806.....101.........729.......@.........292
...........*.....565..................329................*..*........137......$849...=773...........=...*.............*..+..........32......
...359.277..849.....*399..................274....535....348.950.....*...............................................553..607......../.......
.....%.*.................*...146.564.818....*.....*................438..............343..945......85............162.........................
...#...67.374..*593.....740......*......*..553...795..664...$................493#....*............-...............*...971...................
...510.....+........843.......791..277.................*....958....................489..#.................*657.213.....*...610.....193......
........*......#....#.................#.......$..&12....531......167......659*...........521...157*....896...........503......+.......*241..
257..171.245....959........................109................+...............454..................239...../................................
...*...............................................#..........203...%...&..............359.330.846........751...382.985&.........646$..#....
..624........453..................870......890#...662.............371..311...739..........*.......*.............*............=.........817..
..................................*....................250.....54............*......../..........182...........237.....261@.250.............
................743.......946.....943.....414#...80....@.........*..751............159..448..............91.............................&529
683....@....370..............*........569..........$........131...........@34..........*....736.........*...434*929.........127.............
...*.110.....*....48..........644....*....467.................*...............92.....673.......*718.....697.............979.&...............
.745.......503.......288..827.....911.......+.......79..290.191..........$....*....................................230..........517.........
.........%.....551..=.....#...........192.....917..&............597...479.....316.743...%.........#................*........122..*..........
....529.461.../..............793.........*633..*.................%..................=.604.........320.......393..599.........*....717.......
768...*...............=567.....-.144..............545................6....591..............216*.......73..*....*........215+.842............
.....783....855............196......*.........909..*......537.......*......=....435............874.../...902.657........................@449
.............*........%510........28..........*...605.....@.......468............#.....630........................418@..............701.....
......397.....748........../...+........487..521......934...................&992.....-.....160.......477.....-.......................*......
.916.................476.651..462..........%...........*...464......................425....*...........*..531...735....=..878.....853.......
....*...............*.............*..................965...*.........754..3..657.......................92..........@..838...................
.....116.....469...498........537..666....622&............237.......*..........*....204...........242.........&...............599=..........
..............-................../.............283=...........283#.919.........638.*.........452.....*794......204.326...................168
...........................541........................544.............../183........67..903+........................*....75.512..605........
860..............*.........*.............455....730....*......................143................@....-.....=...366.......@......*...+59....
...*..............447....916.....127........+.....*.....60................./....*...............572.658...891...+...300.....674.733.........
.768................................*.-..........522.28.......870.....-....89./......764*...........................*........%..............
............606....*...................798..............298...*......342......430........668.........485.270.265/..893..............=....524
......#.880*.......88..907.........239..........509....=......406.+..........................264........*................829........991.%...
....850.................%.....&913....*...........*...............302..&228.......%601....63*......414....*156.............&...310..........
.............@....184.......=.......260..........748........................149................................895.....697.......*.66.......
..........483.......*....500..970.......88..941...........25.....623...436...*.....................278..........=......*......522..*........
................................*.........*.-.......885....*.......#....$..848........260.........-.....579.........950...........948.......
...........270..........+....$..736.....245.........*....936.512........................*...@..........*.....$.&.........790................
.....................634...764....................488.........#......454...............46.995........344...59..135..........#.@851...@949...
808.......214.............................................610...................................185*........................................
...........*.............+...........812........606..........*.................383..................218...355/................804.@687......
.....751.476......145.....991.314.........................123.....917......434....*.634..&....@.................805....15......*............
......#......25......*884......*..@......526*.................*20....*....*.....328.$....672.245....*392.423$...-.....*......83....484.581..
..............................440.759............124*397...779.......752.303.....................764.................376.806......*....*....
.401..976...75....765.......................%.......................................430...................................*......796....82..
........*...&......*......474...2.-351....287.....=........@.......%....%....*731......$.......=....976.........960#.381..192...............
........808........959.......#.....................322......243...534.134.828............*....95.........241...........*.......388...567....
....$.........511......435.........825..................................................742...............&........%....888...#.............
....53...........-....................$.......-...........................191.....933........454...................649..........=...........
.....................993..430*....624........817.102.......660...............*.../.....157/...*...............................845...........
.....&.....466..692.....*....../.....*.................987.........381....746..................744...........722.........340................
..526.........*...*......74..810....257.........-....../............*...........941..898..................../......769...=...480..$...@.....
........658...338.107..+.................563..550........388*....542.............+....&........112......572........&........*....553...588..
631........#..........641..759......880.@....................740........247....................*...........*............$....310............
..........................@.........*.............888....&........-.....*....3....154....790..24..847/......767......933..............#.....
.....790...684....669............626....324....@.......862......77..+....627..*......*....*.....................809*.............922..913...
......*.............*.....*243..................372..........+.......878.......155.36...656....%..........917.............#.....*...........
....935....184/....888.357.....917..797....293...............427............................665..766.........*.........986.......671........
................................*..................................93.247................$..........*641....598..........................459
........................922*295..664....&..........188%.481..............*.............35.............................806.......107*32..*...
..........261.$113.....................456...................916..480....942.848.....................781*3.146..168....*......=..........222
137.......*.................243..............783*......940......*....*........*......155......*25...........*...$...902........217..........
.../....460.....140..170.........................283..*......647...501...-.359...365.......491.........869..103.............................
...............*......$.........941..................75................282....../...............786*.....*......741.686......24.............
527........................*109.*...522..................*79.....#575...............................810...373..*......*..444*...............
...*..&37...............331.................714*..............................62$...43..%.......................983.446.............79......
886.............................................40.................506.421..............726............171...............676*964.....*......
................651#...301..500..497.......601*......%...263*675......*.......136*56..................*.............836...............264...
........229....................#...&...156.....495..769......................................597.......355.............#..365...379.........
....539.......%...933...................*..138..................402...730.......................*718.......12................$.*............
....*........63...*....................368.....691....................*..............................#...../.....772............116.........
....501............777.......673..728......613.&...467....688.../..526...387...726.......@568.260..456..............*.......64..............
403...........................*.....................*.....*...311.......&.....*....387.........*.......437..$901...744.929..................
...*.......................825.........&...........867.........................994...@........346.......................*.............285...
....260........892*.................294..................................#............................................172.....730...........
........743........610.........954......44@.46....606$..................718......963.970.........863.....772..............*......*..........
284.......*............950.....*..............@..................=.............*......%.............*425.../..=625.....479.305.331...-......
...*...139................*...976........32........-.............655..........233.373.....870..431..................................17......
399...........820........844.........%....../744.353.&...................370........*......*...........@...135..700............*............
....*364.#....../....266...........295................486..........932..........98.311....319..........599....*.&.......98.#....202.........
.........768.........*.........982...........................413....*....185.....+................637.......48...........*.132..............
.....................239........*.....................551.......*38.111....*.@.....778...856*25........605...../....355.........230.........
...105..........*.............879........264....177.....*.783............839.682......*..............*.....-....756....*...415.*.....589-...
.............438....................428....*.........465.....*194....................803....100...955.238..836.........767.%...555..........
.....86....&........702........./..*.......363.........................=630.737#............%...........................................259.
......*....256.......*.......+..57..806.......................591*............................*348....829...................+460............
.....................244....6.....................................789......................687..............................................
"""
```
<!-- livebook:{"output":true} -->
```
"...733.......289..262.....520..................161.462..........450.........................183.............................................\n....*....................*.............707.352....*............/.....................801...@...............333..196........484.635......287.\n....42.........131....913..............*......&..........634..................440..&...............83.....@...........404$..=....*..423.*...\n618.......272....*.........&......547.344...............#............689.589.*....150......382=................................168......433.\n..........=...............253.102*.........#......78.......804..........*........................858.........................-..............\n...69.......*37...510.797...........596.946........#..................................602.175...............203..100..........681.......546.\n...*.....110.....*......*..........*..........396......858=.......381....................*.......246*637..........=..391+...................\n...973........274..551.............576.21@.......$..................*.......................................176............181.883......*...\n.......223............+............................649.701.936...17..482..........80...........210.......+...=.........563.......*...222....\n.373..*..................532....707.......956....@..+.....*......*...........+927.*......698......+....763.........275*.....27..498.........\n....*......................+......*.........*..719....540.........24...=...........39...*...................514.........126..#..............\n.....974.......952*308..@..........965....450............*4.343......772../..............437............=....*............./.....309........\n............58..........840.....34................877........$............189..................*186......657.670................&.......854.\n....22.406..*......883............*......880...........939...................................58.....387..................*..................\n......*....587.........564/......599.......*...........*......................831.891/...552..........$.534+.....%802.975.960.346*..........\n.792+..............828................-807.6...........326....324...722...334..*...........*................................................\n.....................*.......................895..764*.........=...*........*..611..........79.......461@..546*940...818.346..........247...\n....%....473......................288.......*....................932.....590...........918......791..................................*......\n.....621...*........................*....129....425.10.....*.....................419....*.........*...166......#11...................831....\n119........302.832.............159.506................*.229.....493....39...............587....523.......*..........610...805.559...........\n......971.......*..........229*..........961........139..................+....411..................554....26.90.....$........*....-.........\n...........463.615...................315....#...................................-...422.......109.-............*247................231.56...\n..279*159.*...........126...569...............906..20..........990..........27.........%.......*.............................960-......./...\n...........364....812*.......*..$.........812*....*.....369....&......176......................15.346#...#.....908...828..........-650......\n.842*771....................189..9...............42...............897*...............479.................99.....+.......*...................\n................842*356.849...............336.......201................412......./...@...........205....................956....*319.383*....\n...438....&................*......../.......*.../...*....&.......62...*........348..............*....................54.....302.........298.\n......$..318................264.....28...259..824..306...249.......&.392...444............889#..418....945...496..../.......................\n................610.160......................................................%.699...987......................*.............................\n......." <> ...
```
## Part 1
```elixir
grid =
input
|> String.split("\n", trim: true)
|> Enum.map(&String.graphemes(".#{&1}."))
# Let's put .s all around so we don't have to worry about what happens
# when we run off the edge of the map.
grid =
[List.duplicate(".", length(Enum.at(grid, 0)))] ++
grid ++
[List.duplicate(".", length(Enum.at(grid, 0)))]
is_digit? = fn c ->
case Integer.parse(c) do
:error -> false
_ -> true
end
end
get = fn x, y -> grid |> Enum.at(y) |> Enum.at(x) end
is_symbol? = fn x, y ->
c = get.(x, y)
c != "." && !is_digit?.(c)
end
is_touching? = fn x, y, first ->
(first &&
is_symbol?.(x - 1, y - 1)) ||
is_symbol?.(x - 1, y) ||
is_symbol?.(x - 1, y + 1) ||
is_symbol?.(x, y - 1) ||
is_symbol?.(x, y + 1) ||
is_symbol?.(x + 1, y - 1) ||
is_symbol?.(x + 1, y) ||
is_symbol?.(x + 1, y + 1)
end
# For each row in the grid
state =
Enum.reduce(
Enum.with_index(grid),
# Initial empty state. `number` is the value of the number we're looking at
# right now, e.g. 71 when we're here:
# ....*.
# .714..
# ^
# `start` is the {x,y} coordinates of the start of the number we're looking at.
# `touching` is whether this number is adjacent to a part, which will
# disqualify it. `number` is a list of the numbers we've found that aren't
# touching a part.
%{numbers: [], number: :none, start: :none, touching: false},
fn {row, y}, state ->
# For each cell in this row
Enum.reduce(
Enum.with_index(row),
state,
fn {cell, x}, state ->
Map.merge(
state,
case {state.number, Integer.parse(cell)} do
# Not inside a number yet, current cell is not a digit.
# Nothing to do.
{:none, :error} ->
%{}
# Not inside a number yet, current cell is a digit.
# Time to start tracking a number.
{:none, {integer, _}} ->
%{number: integer, start: {x, y}, touching: is_touching?.(x, y, true)}
# Inside a number already, current cell is not a digit.
# Time to wrap up this number.
{number, :error} ->
%{
numbers: [{number, state.touching} | state.numbers],
start: :none,
number: :none,
touching: false
}
# Inside a number already, current cell is a digit.
# Append to the number.
{number, {integer, _}} ->
%{
number: number * 10 + integer,
touching: state.touching || is_touching?.(x, y, false)
}
end
)
end
)
end
)
state.numbers
|> Enum.flat_map(fn {n, touching} ->
if touching do
[n]
else
[]
end
end)
|> Enum.sum()
```
<!-- livebook:{"output":true} -->
```
525181
```
## Part 2
```elixir
grid =
input
|> String.split("\n", trim: true)
|> Enum.map(&String.graphemes(".#{&1}."))
# Let's put .s all around so we don't have to worry about what happens
# when we run off the edge of the map.
grid =
[List.duplicate(".", length(Enum.at(grid, 0)))] ++
grid ++
[List.duplicate(".", length(Enum.at(grid, 0)))]
defmodule GridStuff do
def get(grid, x, y) do
grid |> Enum.at(y) |> Enum.at(x)
end
def find_number_end(grid, x, y) do
case Integer.parse(get(grid, x, y)) do
:error ->
:none
_ ->
case find_number_end(grid, x + 1, y) do
:none -> x
right_x -> right_x
end
end
end
def get_numbers_around(grid, x, y) do
[
{x - 1, y - 1},
{x - 1, y},
{x - 1, y + 1},
{x, y - 1},
{x, y + 1},
{x + 1, y - 1},
{x + 1, y},
{x + 1, y + 1}
]
|> Enum.reduce(MapSet.new(), fn {x, y}, set ->
case find_number_end(grid, x, y) do
:none -> set
left_x -> MapSet.put(set, {left_x, y})
end
end)
end
def get_number(grid, x, y) do
case Integer.parse(get(grid, x, y)) do
:error -> 0
{n, _} -> get_number(grid, x - 1, y) * 10 + n
end
end
end
Enum.reduce(
Enum.with_index(grid),
MapSet.new(),
fn {row, y}, state ->
Enum.reduce(
Enum.with_index(row),
state,
fn {cell, x}, state ->
if cell == "*" do
MapSet.put(state, {x, y})
else
state
end
end
)
end
)
|> Enum.flat_map(fn {x, y} ->
neighbor_numbers = GridStuff.get_numbers_around(grid, x, y)
if MapSet.size(neighbor_numbers) == 2 do
[neighbor_numbers]
else
[]
end
end)
|> Enum.map(fn set ->
Enum.map(set, fn {x, y} ->
GridStuff.get_number(grid, x, y)
end)
|> Enum.product()
end)
|> Enum.sum()
```
<!-- livebook:{"output":true} -->
```
84289137
```
