Add 2021 - Day 8 - Part 1

2021/07/main.kt

@@ -6,10 +6,28 @@ fun main() {
 	
 	val p1 = originalPositions.minOrNull() ?: return
 	val p2 = originalPositions.maxOrNull() ?: return
+	val candidates = p1..p2
 	
-	val cheapestFuel = (p1..p2).minOf { p ->
+	part1(originalPositions, candidates)
+	part2(originalPositions, candidates)
+}
+
+fun part1(originalPositions: IntArray, candidates: IntRange) {
+	val cheapestFuel = candidates.minOf { p ->
 		originalPositions.sumOf { abs(it - p) }
 	}
 	
-	println("Cheapest fuel: $cheapestFuel")
+	println("Cheapest fuel at constant fuel usage: $cheapestFuel")
+}
+
+fun part2(originalPositions: IntArray, candidates: IntRange) {
+	val cheapestFuel = candidates.minOf { p1 ->
+		originalPositions.sumOf { p2 ->
+			abs(p2 - p1).let { steps ->
+				(steps * (steps + 1)) / 2
+			}
+		}
+	}
+	
+	println("Cheapest fuel at polynomial fuel usage: $cheapestFuel")
 }

2021/08/input/1.txt

@@ -0,0 +1,200 @@
+cdbga acbde eacdfbg adbgf gdebcf bcg decabf cg ebdgac egca | geac ceag faedcb cg
+edbcfag ebdca ebgad dagbef cfbed adcg dcgeab ac cae cgabef | gacd ac dgac ebdfc
+gceafb fcabedg ebfd bd ebacf bafcde daecbg dabfc abd acfgd | adb fagdc bd agfbec
+abd cebd bd gcbaf dcafb dface ecgfbda ecdfba fdegca dbafeg | dbecfag bd decb dbgfcea
+ecdagfb eb egfcb gcdbfa dcfeg aecb fabcg afebgd ebg agecbf | bge be abcfge bfedacg
+dbcf gfc fcbdaeg cf bgfced begacd dbgec gdfea cfdeg bafgce | egcfdb ebdgc gadbcfe bedfacg
+efbda dbf fb fegdabc dagbce fcade dfbceg gbadfe abdge gbfa | bafg gbaf bf fb
+afbegc bgcfde dc edagf fcadgb gacbf dgc fdagc dgebfca dcab | dc dcg bgcfa adbcfg
+gfced ebcg fdgceab gdfbe dfcbea ce dfegba dce fbgecd dcgaf | bceg fbegad ecagbfd dfgec
+agbec dgef gfbec ef gfadbc cfgdbe gedfcba cefbda cdfgb bef | bdeafgc gcbdf febdagc fgde
+egabc dcgbef efdbac fdaceg af eacbf cagedfb abdf fac bfdce | bedcgaf dabf gfbdaec afebc
+dbcf efgdca gacdfb bc abfcg dafcbge gbeaf bac gdecba dgfca | gcfab dbgace abcfg dbegfca
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+afgec gefbd edcb edcabgf dcg cdfebg fgbade gabfcd edcgf cd | fagdbe gdcbfe gecaf egfac
+ce ebadg ebc agfcb cdagbe degbfa edcabf dcge gebac egadbcf | ec afebdg gefbad ec
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+debcf degcfa fdgaeb gcdbea cbga cdbeg decga ebg gb dabcfeg | abgecd bg gcbade baefdgc
+gdcbe ga gcae cgdba fgbade fcbedag abfcd gba dacgbe fdbcge | abg dabcg bcfad bga
+dagef geab agdfbe dceaf gcdbef egbdfca fabgd eg egf bcgfad | dgafb ge gfdae aedfg
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+dagbcf debfgc aegc bag abgde dbacge dfaebcg bdecg ag adfbe | ga gcaefdb gba bdgaec
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+abgdc da gadbec gdbcf dag egbac dcea becfga gafebd dcbgafe | acgbde gdfabe dga dag
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+ac efcbd gedfca ace febcad cabde gcdbef bgade bdegacf cfab | befcd acbf ceagbfd abdecgf
+dbfagc abdce fgea gab ceagb fbcega gecdfba ag gfecb efcgbd | cgadfb aefgbc gaebfc efag
+cebfd bdfeag fgc edgaf gc dgca cdebafg gcfde geafcd feacbg | fcgde gcdeafb adcg gfdaceb
+gcebadf cebdag egcfda acfd cdegf fgecba cf dgeac fcg fdgeb | decfga fdac egabcf ecabdg
+fgabc egbfcd eaf gead dfegb edgcbaf agfdeb acbdfe ae afgeb | gdebf dgae gebdf efa
+gcadbe bacgd gcbafed gdcef aebfgd age aecgd cabe dfbgac ae | dcgba bace age acbe
+fgdca gcabfd dfea gcefa ecdgaf adfbgce cae gecabd cgebf ae | ae fcegb acgdebf acbedg
+acbdgfe gdcfa aecfg abfdc gd fgdb efbacd gfdbac gda bcedag | dga fgdb bagdcf gd
+fg dagfcb gfeac cegba dfceab adfgbec fged gfacde fcdae fcg | dfge fgc acgef gcf
+agfcbd cbagef edbfg ecbgafd bagec fageb cabdeg fa ecaf abf | efagb debgf af caebgf
+afecdg decgfb geabd bgd afbd bd caegb fgacbed feagd gfaedb | gcafed cebfdg fadb cfaedg
+cedfb dgfeab ecgba fcdg fgb befgc fdaebc gfebcd fg adcgfbe | fdgc afbdcge cgdbef cefbg
+defc gebcf cgdbfa fc cegab bfdeg dgcfeb fgc bgadfe dagcfeb | fcde bedgf gfc gfdbea
+badceg bea gbafc dafge cfbdga geafcb cfbe gabfe eb gfcdabe | eba bfce fbec eafcgb
+fbcedg gf aedcg decbf gfeabd efg gbcf faebcd eadbgfc efdcg | fge dgcbef fge cfgb
+cbdeg bfca ca bgefa aebgc fcgaed gcfbea gac cfegabd defgba | gcaeb gebfda bgedfca ca
+ecfd cabdg bcfeda cdeab ed eafbgc dae gaebfd ceafb cfgdaeb | cefadb befacgd ecfd gbfaced
+cgdea gcfabe afecgbd becgdf eb abgce abef bce fcgab dcbfga | bgfdce egcfbd ebcfgd ebcdafg
+fcbed fbged fdag gd egdfbac gacdeb egbaf dge cbeagf fdbgea | deg dg dacegb cdgabe
+faegcbd aed gfdba fdce gfacde ed adfge dcegba acgebf fcaeg | aedfg cebagf de de
+dbcega geabf gcebfd deg cfbade dg debgf dgfc dcfbe ebadfcg | cdfaeb deg gfabe gcbedf
+bgecd bafg efdab ebdcaf edfgab gf dfg degbf fcgeadb aefgcd | gabf bdgfe fbdae cbedfa

2021/08/main.kt

@@ -0,0 +1,35 @@
+import java.io.File
+
+fun main() {
+	val records = File("input/1.txt").readLines().map { line ->
+		line.split(" | ", limit = 2).map { it.split(' ')  }.let { Record(it[0], it[1]) }
+	}
+	
+	val simpleDigitCount = records.sumOf { r -> r.output.count { it.length in UNIQUE_SEGMENT_COUNT_TO_DIGITS } }
+	println("Total appearances of 1,4,7,8: $simpleDigitCount")
+}
+
+private data class Record(val patterns: List<String>, val output: List<String>)
+
+private val DIGIT_TO_SEGMENT_COUNT = mapOf(
+	0 to 6,
+	1 to 2,
+	2 to 5,
+	3 to 5,
+	4 to 4,
+	5 to 5,
+	6 to 6,
+	7 to 3,
+	8 to 7,
+	9 to 6,
+)
+
+@Suppress("ConvertLambdaToReference")
+private val SEGMENT_COUNT_TO_DIGITS = DIGIT_TO_SEGMENT_COUNT
+	.entries
+	.groupBy { it.value }
+	.mapValues { it.value.map { e -> e.key } }
+
+private val UNIQUE_SEGMENT_COUNT_TO_DIGITS = SEGMENT_COUNT_TO_DIGITS
+	.filterValues { it.size == 1 }
+	.mapValues { it.value.single() }

README.md

@@ -37,3 +37,4 @@ The versions should not matter, but I used Visual Studio 2019 with `MSVC v142 (1
 | 2021 |  05 | Kotlin   |
 | 2021 |  06 | Kotlin   |
 | 2021 |  07 | Kotlin   |
+| 2021 |  08 | Kotlin   |

build.gradle.kts

@@ -50,4 +50,5 @@ sourceSets {
 	make(2021, 5)
 	make(2021, 6)
 	make(2021, 7)
+	make(2021, 8)
 }