day 8

8/README.md

@@ -0,0 +1,74 @@
+--- Day 8: Treetop Tree House ---
+
+The expedition comes across a peculiar patch of tall trees all planted carefully in a grid. The Elves explain that a previous expedition planted these trees as a reforestation effort. Now, they're curious if this would be a good location for a tree house.
+
+First, determine whether there is enough tree cover here to keep a tree house hidden. To do this, you need to count the number of trees that are visible from outside the grid when looking directly along a row or column.
+
+The Elves have already launched a quadcopter to generate a map with the height of each tree (your puzzle input). For example:
+
+30373
+25512
+65332
+33549
+35390
+
+Each tree is represented as a single digit whose value is its height, where 0 is the shortest and 9 is the tallest.
+
+A tree is visible if all of the other trees between it and an edge of the grid are shorter than it. Only consider trees in the same row or column; that is, only look up, down, left, or right from any given tree.
+
+All of the trees around the edge of the grid are visible - since they are already on the edge, there are no trees to block the view. In this example, that only leaves the interior nine trees to consider:
+
+    The top-left 5 is visible from the left and top. (It isn't visible from the right or bottom since other trees of height 5 are in the way.)
+    The top-middle 5 is visible from the top and right.
+    The top-right 1 is not visible from any direction; for it to be visible, there would need to only be trees of height 0 between it and an edge.
+    The left-middle 5 is visible, but only from the right.
+    The center 3 is not visible from any direction; for it to be visible, there would need to be only trees of at most height 2 between it and an edge.
+    The right-middle 3 is visible from the right.
+    In the bottom row, the middle 5 is visible, but the 3 and 4 are not.
+
+With 16 trees visible on the edge and another 5 visible in the interior, a total of 21 trees are visible in this arrangement.
+
+Consider your map; how many trees are visible from outside the grid?
+
+Your puzzle answer was 1662.
+--- Part Two ---
+
+Content with the amount of tree cover available, the Elves just need to know the best spot to build their tree house: they would like to be able to see a lot of trees.
+
+To measure the viewing distance from a given tree, look up, down, left, and right from that tree; stop if you reach an edge or at the first tree that is the same height or taller than the tree under consideration. (If a tree is right on the edge, at least one of its viewing distances will be zero.)
+
+The Elves don't care about distant trees taller than those found by the rules above; the proposed tree house has large eaves to keep it dry, so they wouldn't be able to see higher than the tree house anyway.
+
+In the example above, consider the middle 5 in the second row:
+
+30373
+25512
+65332
+33549
+35390
+
+    Looking up, its view is not blocked; it can see 1 tree (of height 3).
+    Looking left, its view is blocked immediately; it can see only 1 tree (of height 5, right next to it).
+    Looking right, its view is not blocked; it can see 2 trees.
+    Looking down, its view is blocked eventually; it can see 2 trees (one of height 3, then the tree of height 5 that blocks its view).
+
+A tree's scenic score is found by multiplying together its viewing distance in each of the four directions. For this tree, this is 4 (found by multiplying 1 * 1 * 2 * 2).
+
+However, you can do even better: consider the tree of height 5 in the middle of the fourth row:
+
+30373
+25512
+65332
+33549
+35390
+
+    Looking up, its view is blocked at 2 trees (by another tree with a height of 5).
+    Looking left, its view is not blocked; it can see 2 trees.
+    Looking down, its view is also not blocked; it can see 1 tree.
+    Looking right, its view is blocked at 2 trees (by a massive tree of height 9).
+
+This tree's scenic score is 8 (2 * 2 * 1 * 2); this is the ideal spot for the tree house.
+
+Consider each tree on your map. What is the highest scenic score possible for any tree?
+
+Your puzzle answer was 537600.

8/input.txt

@@ -0,0 +1,99 @@
+231123311143433334111323513140220312430352020530355453134243354254345525504344520412234022441201231
+002313303032210031340314312003010320224404022622605552013026333142351022440040305400004242132311121
+220330201413404422305112240330213320021136124315415335033123035640315511030034514131440424021313030
+201320204042120231444423450514444264034132022532310222544264033660224245455501245254224301113033202
+100230132320401153153211332210134066253434230603403642463504006006105221540233444530342314043014303
+122032442431414332522045441015500404344203644233226634442443603306655031345051541032504421424133033
+202321031434355013211523304504664140162101106663501334114500001506012426201040202213400414410420443
+033422404010423322510522632054006500415024100365442766531456202021112062035410413353104310042243312
+110443431341401301233403206566150220000024461521454711652314543050111414550422244110103411011111044
+201203422242133202032302263406105000637616447267624727521265126530162241350166442154043253234041313
+104022033221031042241034106164466623536612244376774564121253574772146361562004241421223514023220400
+440414310500545052512332656122163241446422624364551456541317446567332305362006013160044233035333032
+210004115150024101145654165555423566515754711264245263541734173357434433263303155546120144222240002
+030042432414255562126315563211647645153362721512142763677766742114561322465216641361020150545534412
+403123015321050535251565357633562474213343726145764737476652716513162657627334001426643231115312122
+114301034250403323442564327645166772164175757584482225242282452331322551462150315355210411522315334
+342135502250325230031455573651146635678748778856468367545852536126334772633520613166345055125343121
+240331414023533433311117124527727134563268363765626876836874354585566662473377025500230041031012433
+435521420116206160651166217552425745555244872556778684862854644355351636153154772201634233245254141
+430142200342652562361156566471575782662428747225633244384252643488668173133776753050305455521012404
+101154055404461145474553357357435226287655284867536556382736847785686582546336527411161654600510522
+125205523012146541452325155713277563445585483226638265875362343584672325666362655372014353034500103
+152205531442652200416553617228567268556458664338963688659762235834558825512465454776303604222502325
+233343103643212413761233124526836322436345686967999467774633437656482385721431646313026222325053512
+501320340461623523537621263368458686388686939337494776585685787477573454446327641637323555161002134
+515322360042621777412121437723477582693859378967469987843385364968522276542363545157536002411505525
+205513414500467712163114548784778857594533965478846483595953669558926378465254653724652136460101315
+041100604001336362642258742846457779439797634646658538538454373556384447328632577227354404322115241
+330432606365061456254442526383759337794885884574763495378836935647477758875783835723357120346646344
+033216032220115616576773874887677934937366554498565984797377599998564672852636275344552444234312443
+215111363343756276436445667785966574594365559764868559544885789668635945537522848776576443061535203
+415106311514725425418676378769957879764874855455454784746657855964963336748226643736534746104406622
+152263045613177665648375528588468936695497559865474888988744766995756979628325554634164515561435210
+311405136106436751167488647478374739958766847885898896654578454764947876647224765542171351625331402
+131443421361717252678663268356687689566784598894969544588495896879354855698683874233631212742011640
+114520223332777465223364875648649544757874847599865776469577589798756533866786726347542316613434561
+156464406534124114847235838367885658894975444878866689568885867449774994866957448867553672323050532
+341262503143467744668835539889446596657688869875588789855844648987585544678955565272321116365045416
+354062244564521725625863867798447588968959666555598779795685694965878538389768366485677142523000201
+035003352561512182538484597854465568656549866688667696565599674549859567576467434286677737322650166
+113555506117316553752425399466445855596576885595765599877985868784676496886647746336332614245114064
+260525047433675637362744744746965596745875587686787655888585764566965659969486384433847371754462664
+213036656715765765336849567376558777645985876768858575697557669689449869597695848484552253325663114
+225226243535142385386537866646748879665589678668868867676957765864677746465394355566587567413633214
+652500055731517563452799369639476546488879888978888969876696578989794546483797652865282261755565063
+024003237232476584354267844688644488895875886897676966666978587554448587637653957856324154444551030
+211124217521676866657866967469554969776798799797689778796897569888647694545836942562787275723446131
+510442553712443855247736378387867488559767587798878667777576886666856475837476734748582622223223501
+220055237372748256763577645667969449698885959788976987676895869577946945433688788847875644234514060
+050143342621224332656354344358485996676998697799776866879788595858756757845396823522835523664231326
+316046134444356827463638837499878598587857688887687679866679788667679468887353632246342771363423252
+641355624314462855644343484387958776657888786678877699879886989985667894575797876524556757272165011
+423566165222552367487595663974765677799955758979788776886679966565888579769359357224677534537141651
+240143127214453852854697498688544489889658768667779776696897657765756684836674633574744751223604160
+104532363252255383665298956339597974787695766667666978979989695967556679858735728553776467644562216
+160252112156645687864737579876579556659787688786899869685678598778546447383854634524285537422561544
+144631662137632684444797985884675589666896557778686979865796777678645854558456577835321115175636202
+444031263653662743278288954355878959587987677987886889875889867959766986673565324856524455513626620
+452205301637437747724748457543645895655589955779998675577599655454594858884369778248235144135565401
+234535635453237468746769753649999785595567569977657769578765567659965434939874344677212223116135166
+444105464456237738335639358986997765965755775795789756667588966656447534349493346336265231236016106
+503403266731262767562768396436564565885788896959978587865898986564897945435443888864226345570560536
+103660362732546153332236469356634769484684955899875998959669449899894843593367345252531154430031141
+433313341743147116622563299974444465696459985877785895698975778574955544587934636354374541670342234
+104336613227653354433482854646447388478769484788767768848459746995748858889722867652664746756650532
+124455315366571475275687734947899445845697785949895887444748948474379964335877536646374747202233561
+122315236055236642327253763779969358698655997694647598666594646559644756476585247722143334262161245
+345552103454725471248265478834399638774649598795666886868748785677755789387875583563314137065031002
+410322332227162535482236366633968648797455484884875946656868448359466347548777783274637756643120140
+403311304541576275564322776478376978759955444596858985968559893674539657357256874326242333044431503
+343563440503243435458363728735763359357947785769684969489758498534634678545673786613447310065143224
+113152516545452341611442573535284843994635866487445768694794596986745755247432267662136265543340113
+154353641300537551455688753472457857675989577763574873858487488936987572523488633414765434041263333
+242422354645546262556563346488438493576836888373556749869537946778585772522787163331611051133204335
+303235665440603551575424253236433534846667769999767585833386583775345834273536341323426263551352510
+053030406033265327572256285227386337843368688683848398367483486368775387544552557427526262124232115
+102311254415365421253455216342557452425939763556975494953887935476865466466552773335155141256501043
+544415223520360203126673345687523838428633677773987658675364824355522532266552771672433466302033554
+444445546303415444242143251255326422583427368356749366396356862636866376422762775321530066462133350
+335014151363326422315426733476578288542533458836887285533354524248552822114455466545010246505051525
+025113253162211635452547563652488548824353262345325252722658275255427883666252736546213552414312322
+403352135452042501437331142677262273453326783245758487233657647242354557216175336246362031212324354
+334512051451011330411642277436174585456448264622345773745358252527373173277211514531553566055210450
+443525552450034602520313313415545646578283527627247267654435357633251644633137546562565211320440433
+144442150012541262552434267445764164122522886624765246373687767154314415153110143502445150443431031
+202425401220411403326146273315422521647643672468433378637542765356644551525410533164460005203522121
+440445442434522260350134113673244167326723517373484263521722456627265561124205112001040324024302200
+133241444214340263233345225362331635776735317726464122445365756467666216601624122203641551304332133
+212333420124003410012341433556217433677653363453333271575214145154125371146442146630233421151232024
+324240103540013240405025100243405535224233412432636577232175773454226631111265416431321002353231404
+330042444125504323431136353162410146747642365212471233563311373471322005154000234515441441033000211
+311222123304343401241325355353252011244755553111776513357461242252101665160165003031522555503110121
+222423234211032113215030002041036266501244776723164247523537502152150623662614404111432355402044330
+120223310302022255244105120215044423010054135641724271263340546024016502036452454514514012131010434
+001000231212004145205543502526310535133132351322613330166226622135343154016155251111332512413400430
+300023321142325420044420540430554235664134336551105200015263030025634562522251053500542342334114401
+020110224214134125154505403134561022633204410210043364116436221455124661035142022431003221032202111
+110333213443142104354013214103233265610323413403454633321354646456612411442532034115333321011400012
+202023244334034212011253451025324523366442241613146204642341061310011354032001004431232121344412112

8/sample-input.txt

@@ -0,0 +1,5 @@
+30373
+25512
+65332
+33549
+35390

8/src/index.ts

@@ -0,0 +1,92 @@
+import { FileHandle, open } from 'fs/promises'
+
+function sceneToTheRight(row: number, column: number, rows: number[][]): number {
+  const numColumns = rows[row].length
+  if (column === numColumns - 1) {
+    return 0
+  } else {
+    const height = rows[row][column]
+    const blockedAt = rows[row].slice(column + 1).findIndex((cell) => cell >= height)
+    return blockedAt === -1 ? numColumns - 1 - column : blockedAt + 1
+  }
+}
+
+function sceneToTheLeft(row: number, column: number, rows: number[][]): number {
+  if (column === 0) {
+    return 0
+  } else {
+    const height = rows[row][column]
+    const blockedAt = rows[row]
+      .slice(0, column)
+      .reverse()
+      .findIndex((cell) => cell >= height)
+    return blockedAt === -1 ? column : blockedAt + 1
+  }
+}
+
+function sceneToTheNorth(row: number, column: number, rows: number[][]): number {
+  if (row === 0) {
+    return 0
+  } else {
+    const height = rows[row][column]
+    const blockedAt = rows
+      .slice(0, row)
+      .reverse()
+      .findIndex((row) => row[column] >= height)
+    return blockedAt === -1 ? row : blockedAt + 1
+  }
+}
+
+function sceneToTheSouth(row: number, column: number, rows: number[][]): number {
+  const numRows = rows.length
+  if (row === numRows - 1) {
+    return 0
+  } else {
+    const height = rows[row][column]
+    const blockedAt = rows.slice(row + 1).findIndex((row) => row[column] >= height)
+    return blockedAt === -1 ? numRows - 1 - row : blockedAt + 1
+  }
+}
+
+function calculateSceneOfTrees(rows: number[][]): number[][] {
+  return rows.map((row, rowIndex) => {
+    return row.map((_, columnIndex) => {
+      const right = sceneToTheRight(rowIndex, columnIndex, rows)
+      const left = sceneToTheLeft(rowIndex, columnIndex, rows)
+      const north = sceneToTheNorth(rowIndex, columnIndex, rows)
+      const south = sceneToTheSouth(rowIndex, columnIndex, rows)
+      return left * right * north * south
+    })
+  })
+}
+
+function maxScene(scene: number[][]): number {
+  return scene.reduce(
+    (rowMax, rows) =>
+      Math.max(
+        rowMax,
+        rows.reduce((columnMax, calc) => Math.max(columnMax, calc), 0)
+      ),
+    0
+  )
+}
+
+async function solve(file: FileHandle): Promise<void> {
+  const rows: number[][] = []
+
+  for await (const line of file.readLines()) {
+    rows.push(line.split('').map((c) => +c))
+  }
+
+  const scene = calculateSceneOfTrees(rows)
+
+  console.log(maxScene(scene))
+}
+
+async function run() {
+  const input = process.argv.slice(2)[0]
+  const fd = await open(input)
+  await solve(fd)
+}
+
+run()