Done day 9

diff --git a/advent-of-code21.cabal b/advent-of-code21.cabal
index c3b897768f6ff9438bc7e838bce5205876eac704..9e50851364a5fd95e2942403189437b8858d37bd 100644 (file)
--- a/advent-of-code21.cabal
+++ b/advent-of-code21.cabal
@@ -124,3 +124,8 @@ executable advent08a
   import: common-extensions, build-directives
   main-is: advent08/Main-longwinded.hs
   build-depends: text, attoparsec, containers
+
+executable advent09
+  import: common-extensions, build-directives
+  main-is: advent09/Main.hs
+  build-depends: array, containers

diff --git a/advent09/Main.hs b/advent09/Main.hs
new file mode 100644 (file)
index 0000000..4cd269e
--- /dev/null
+++ b/advent09/Main.hs
@@ -0,0 +1,85 @@
+-- Writeup at https://work.njae.me.uk/2021/12/09/advent-of-code-2021-day-8/
+
+
+import Data.Array 
+import Data.Char
+-- import Data.Maybe
+import Data.List hiding ((\\))
+import qualified Data.Set as S
+import Data.Set ((\\))
+
+
+type Coord = (Int, Int) -- (row, column)
+type Grid = Array Coord Int
+type Basin = S.Set Coord
+
+main :: IO ()
+main = 
+  do  text <- readFile "data/advent09.txt"
+      let grid = mkGrid text
+      print $ bounds grid
+      print $ part1 grid
+      -- print $ lowPoints grid
+      -- print $ breadthFirstSearch grid (S.singleton (4, 6)) S.empty
+      print $ part2 grid
+
+mkGrid :: String -> Grid
+mkGrid text = listArray ((0, 0), (r, c)) $ map digitToInt $ concat rows
+  where rows = lines text
+        r = length rows - 1
+        c = (length $ head rows) - 1
+
+part1 :: Grid -> Int
+part1 grid = sum $ map (riskLevel grid) $ lowPoints grid
+
+part2 :: Grid -> Int
+part2 grid = product $ take 3 ordSizes
+  where lows = lowPoints grid
+        sizes = map (basinSize grid) lows
+        ordSizes = reverse $ sort sizes
+
+riskLevel :: Grid -> Coord -> Int
+riskLevel grid here = grid ! here + 1
+
+lowPoints :: Grid -> [Coord]
+lowPoints grid = filter (isLow grid) $ indices grid
+
+isLow :: Grid -> Coord -> Bool
+isLow grid here = all (> this) nbrs
+  where nbrs = map (grid ! ) $ neighbours grid here
+        this = grid ! here
+
+higherNeighbours :: Grid -> Coord -> [Coord]
+higherNeighbours grid here = filter isHigher $ neighbours grid here
+  where this = grid ! here
+        isHigher there = (grid ! there) > this
+
+basinSize :: Grid -> Coord -> Int
+basinSize grid basinSeed = S.size $ breadthFirstSearch grid (S.singleton basinSeed) S.empty
+
+breadthFirstSearch :: Grid -> Basin -> Basin -> Basin
+breadthFirstSearch grid agenda basin
+  | S.null agenda = basin
+  | otherwise = breadthFirstSearch grid agenda' basin'
+  where here = S.findMin agenda
+        candidates = (S.fromList $ higherNeighbours grid here) \\ basin
+        basin' = if (grid ! here) == 9 
+                 then basin
+                 else S.insert here basin
+        agenda' = S.union candidates $ S.delete here agenda
+
+
+neighbours :: Grid -> Coord -> [Coord]
+neighbours grid (r, c) = filter (gValid grid)  
+  [ (r + dr, c + dc) 
+  | (dr, dc) <- [(-1, 0), (1, 0), (0, -1), (0, 1)]
+  ]
+
+gValid :: Grid -> Coord -> Bool
+gValid grid (r, c)
+  | r < minR = False
+  | c < minC = False
+  | r > maxR = False
+  | c > maxC = False
+  | otherwise = True
+  where ((minR, minC), (maxR, maxC)) = bounds grid

diff --git a/data/advent09.txt b/data/advent09.txt
new file mode 100644 (file)
index 0000000..b943c4c
--- /dev/null
+++ b/data/advent09.txt
@@ -0,0 +1,100 @@
+9987675345698765453987654321234589999899878923493212345678999998656782467898999899878301234578998787
+9876543234789765322398743210123567898789767899986101239899789876543101567897898798763212355989987656
+3987784014897654310987654331235679965697644998765232345997654989765212799956999679854343466799976545
+2199875323998765421298776542346789434595433498754345456789543499876353489549876542975858977899876439
+1012965439899896432359987667457896546789322349987656987898932445987454578932987621986767898943989598
+2125976598798989943467898876589999858899910959898767898976101234598966689431298320987898999432399987
+3234987987656579894578989987679998769999899898769879999965422345679298995420139434598999896543459875
+4346799876545456789679877898789769878989798799656989899876563496799109989591298548999689789656598764
+5956998765434345698989765679895456989678679678943496789988689989898997979989987657987565698787989543
+6899898764321234567999876989954345696534598789432134679999799976987656765778998769766464989999865432
+7987679653210155789999997899875456789323999899521012345899899765698943254667999898954353578999654321
+9696598654323234589788998998986567898919894958933423456789999753459892123458998987893212467898765432
+8543498765434545679567899987987679987898743147894934567898989432398789334767987876789101298989876543
+7656789878545656789338989876598789986797654235679895678997878941987678975879896545698914345678987654
+9868998989656877892129678965439899975498754346998796789986867932954569986798765434567895458989998765
+8979987798787898921012567894321999874329985459876589899985457899873458987987654323469986567899869876
+7899876549898959999923456789432398765909876567987678999875322987654567898998773212378997698998754987
+6534997831999943987894567897543999899899987878998789789964201298765678919679654323456789799987632399
+5424598942689899876789678987659899988788999989019895699865362349986989103498795434567899899996549989
+4212349653498789765699989798798789877697898999999924789976457899798993212379986747698946999897998878
+5334569878989678934998995679987678954545987899789935689987567987649898763467897858789235798789887867
+6446878989876569976897893459876567893239876797689898789397679893234789654598998979999546999698785458
+7557989199987457898956789998984348994124965323486789895498798789123569875989109989898969898598654345
+8998994398796346899545699876543236789549876412345678979569987679023456989878992398767898767469643234
+9999689987654235695434689987652125678956987954456789768979876568994568999867989987659999955398759345
+7887578976543123489545679698983234789768998765677993457899765456789878997654878998767899843229898956
+6543469998768245678956789529865445899879999896798912349998987347899989989653467899879998732019987897
+7672398999875456989767895439876556789989989999899102356987798456789899878932356789989987643498976789
+8954987899986567899878976546989667993498979978976212469996549567895798969991245699899998754987685698
+9769876989987898901989997656898789101997768769895433498765439878934987656789346789788999869876564567
+9898765778998979312397899767999893249876753656789656569976524989423976546789498997697986998765473456
+3987654569789765434456976978999974756965432345678987678987734694319887635689989998456894219874321567
+2198733477678978645797895989989865669876543766799998789599848789998765212678979999367975323985432378
+3989821234568999756898934599878976798998754567898999897679959899899874323599867895459876434596543458
+9876432347679549887969423498969987897989865698997899979898767998798765435679756899567987546987654567
+9876543489789832998953210987658998996579878789876588965939989987659987546789645688979987657898785678
+3987654579898721239998723976547899987467989999995477894321098765545698687895436577898998898999896789
+2398766789989654359899644597656999876345697679654356965434197543434989798954323456987899939998987893
+1239887894678965498788987698987999765234789598765467896545976532129879899996534567896789123976798912
+0945998923567896997687898999298987653123696439876588987679876549098765945987965778945693239875459901
+9896789434678999876575999899399199762064594321987678998789989698987654326599878989238789459954345899
+6797898645789998767434598798989349872165689410198989769899898997898543212367989994345678998986254678
+5789949756894987654323497687878959989278796521239797653998767876799654302456999965456899987432123689
+4569439887893998799934598576967898995478897432345698992989545665698775212567899876697899876543234567
+5678921998969899987899974475459997898567998945456789989878932124569854323498976989989965987654345678
+6799990199656789876798863212349976987678999896897899879767893234698765434578965699878974598785458789
+9899989989543298765987652101267895999799998789998998968456789345999879545679854598767943459987569893
+3998979678932129894598543323458934889934987698999987654345895469876997656789765987659894567998678942
+1987667569892099989679656445667895679899876597896596543256896567989998789899876798547689978999789531
+9876553456789989878998767986898996798788995456789987752125789678998999897999987899534567899989898940
+8765432345679878967999899597959789987576789347899876543234589789987899975689999987656789929876967891
+8764321234698766556899995329345678987455678956789989684348678999876798764567898998769893212975456932
+9863210123459654345688989910258789876323589969894398765457789998765679923459987869878999109864349894
+9854525234598743234567979891345897995474567898989239878767899997654567895678996555989998919753239789
+9765434545987655455679865789457896986567678967878946989878959876543456789789789434599987898954398679
+9896565656898766767999954567978965497678989656567898998989245988652346799894698765679876767895976532
+9987879768999879879878323489989654398789893432349899987690159899721278967923989876798965456987987699
+8998989879988989998965412397898765219899762101234789996521998798754367899999878987987654347898998987
+7659395989876897987654323456789898323998753242345678989439887699865456899989769999876543236789019986
+8543214598765456798987654589896987536789894355456989879598754589876967999877658999997655345678998965
+7654323679876578969999865678945698545678976566567898769987653479989898998766546898998786457799987654
+8795498793997989657899976789234987657799987677678965657898794567998789987653234567899898568899998723
+9989989932398996546789989890123498968989998788789654346789887679899678996442123458901987678999899812
+9878879993989875237899999989254989979878999899898766869895998997676567894321015667892398789999798923
+7767767989878943123978999878969978998967899922939878998953219876565456976534124578943469999988697654
+6553459876767894234568986767898767987656789210125989987994101985432389997645234567894590129876598785
+5432345985458995679799875456989659876545456991234899876789919996676569987656545678965989239988439986
+4321359894346789789987654345678943965434345789546799765679898987787878998787656989879879998895321298
+5430198765497899894298763234567899876521234899987987654598787999898989109898767899998967897654210129
+6541679876989945999987654345678989987752345678999999766987656579999793212999878999987656789775323234
+6432589989877899998998765476989978998843459789998939878996545468989654329989999998798787894989876545
+7543458998965778987679976687898767898754678999987923989876432345678976498978989987659898943497987676
+8654567987854567896563987798998656899865789019876894599987321238789098987967878998743989932346798888
+9766779876543488997432398899987745679877892198765789998765450139989129876754568999974567895459999999
+9877898765632356789543459921096434567988943989654567899986521234678998765323467899865679976598897912
+9988987654521237989699567899987558978999659876543457899987634656899986544212456789877889987987656893
+9999996543210357678987998998998667989431968997652346998998785667901997432101348995998994398996545789
+8932987987631234589476789987689978999599878994321345997899996778929899546712467894239987469997434679
+7891098876546349679345678965578899998989989989935459876979897889298778994324578943190296599989323567
+6989129989865478993234567893456799987878998776896567965468789990199656989435678954989987989978934569
+5678949999976569310123689932345689876569899565789778984345688999987645678945789769979999878767897698
+4567898999987679453294594321017992985498765434698999993234567898765434899656899998768999765457898987
+7698987898799789564989695532399891996309899323456789832125678919876325999797999887657987654346789876
+8999876789654998679879989649989799876212987437899898761012348901985476789898998765431298743235689985
+9899965689543249998765679998767678965429876556945987652125667899876787899979459963210139852123798954
+8788754799932129879654587789656567896578987987899876543234799998989898998764349854321298764234567893
+7656543458794298965443445678932456789789598998901997654345678997693939789943298765432359879876899952
+6543252345679987654352237899751577899895459789212398897656889986542124599892109887545456989987896541
+8432101489989999875210128932967698998901345699924569998767994987431023999789213998676569995699965430
+7654312678999998996321239999878789767892396989895678989879993976545129897678954598789678934567976521
+8976433589998767987542356789999891557789989978789789467998989897685398789569899989899789325679897432
+9987544567899655698653468999987910345679878765678992345987878799896987667348798976949895434599789545
+9999655778999543219766567899876621234598765454567891249876567689929876543237667895435976565987679656
+8798789989988959309877678999765432545699654323479910134995456578912997632123456789523498878996598977
+6549891299876898912988989789876547686987543212567891239984323469329876321014567898654569989985456799
+1234932997764667893499995678987658798998654403459932398765012478998765432125678979866789699876345678
+0356799876543456994567894567898967899019873212378993987654139989219876843336789565977896579843234589
+1235789987532345789978943456899878978929764323456789398543248892101998765459895434598965498765445678
+2356897698421234567899432346789989767899875435668891239654356789432789887567976323699654329876786789
+3567896543210246788987541457892499848921986546879910129767568996545699998678988434789543210989897899
\ No newline at end of file

diff --git a/data/advent09a.txt b/data/advent09a.txt
new file mode 100644 (file)
index 0000000..610bad9
--- /dev/null
+++ b/data/advent09a.txt
@@ -0,0 +1,5 @@
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
\ No newline at end of file