1+ package adventofcode2023
2+
3+ import java.io.File
4+
5+ fun Pair <Int , Int >.add (other : Pair <Int , Int >): Pair <Int , Int > =
6+ Pair (this .first + other.first, this .second + other.second)
7+
8+ object Day10 {
9+ private const val STARTING_CHAR = ' S'
10+ // Constants for marking flow direction in the second part
11+ private const val UPWARDS_DIRECTION = ' U'
12+ private const val DOWNWARDS_DIRECTION = ' D'
13+ private const val OTHER_DIRECTION = ' O'
14+ private const val NOT_LOOP = ' .'
15+
16+ private val inputs = File (" resources/adventofcode2023/Day10.txt"
17+
18+ // Vertical pipes' first element is the direction that flow is going from so that the pipe is going upwards, the second is downwards
19+ private val pipes = mapOf (
20+ ' |' listOf (Pair (0 , 1 ), Pair (0 , - 1 )),
21+ ' L' listOf (Pair (1 , 0 ), Pair (0 , - 1 )),
22+ ' J' listOf (Pair (- 1 , 0 ), Pair (0 , - 1 )),
23+ ' 7' listOf (Pair (0 , 1 ), Pair (- 1 , 0 )),
24+ ' F' listOf (Pair (0 , 1 ), Pair (1 , 0 )),
25+ ' -' listOf (Pair (- 1 , 0 ), Pair (1 , 0 )),
26+ ' .'
27+ STARTING_CHAR to listOf (Pair (0 , 1 ), Pair (0 , - 1 ), Pair (1 , 0 ), Pair (- 1 , 0 ))
28+ )
29+
30+ private val verticalPipes = setOf (' |' ' L' ' J' ' 7' ' F'
31+
32+ private fun getCharAt (position : Pair <Int , Int >): Char =
33+ inputs[position.second][position.first]
34+
35+ private fun getStartPosition (): Pair <Int , Int > {
36+ for (y in inputs.indices) {
37+ val x = inputs[y].indexOf(STARTING_CHAR )
38+ if (x != - 1 ) return Pair (x, y)
39+ }
40+ throw NoSuchElementException (" Start position not found"
41+ }
42+
43+ private fun getFirstPipe (startPosition : Pair <Int , Int >): Pair <Int , Int > {
44+ pipes[STARTING_CHAR ]?.forEach { direction ->
45+ val position = startPosition.add(direction)
46+ if (pipes[getCharAt(position)]!! .any { getCharAt(position.add(it)) == STARTING_CHAR })
47+ return position
48+ }
49+ throw NoSuchElementException (" First pipe not found"
50+ }
51+
52+ private fun getLoopLength (): Int {
53+ var last = getStartPosition()
54+ var current = getFirstPipe(last)
55+ var counter = 0
56+
57+ while (getCharAt(current) != STARTING_CHAR ) {
58+ val newCurrent = current.add(pipes[getCharAt(current)]!! .first { current.add(it) != last })
59+ last = current
60+ current = newCurrent
61+ counter++
62+ }
63+
64+ return counter
65+ }
66+
67+ // Returns a map with only the loop consisting of upwards/downwards/other markings
68+ private fun getLoopDirectionsMap (): List <List <Char >> {
69+ val directionsMap = List (inputs.size) { MutableList (inputs[0 ].length) { NOT_LOOP } }
70+
71+ fun updateDirectionsMap (position : Pair <Int , Int >, char : Char ) {
72+ directionsMap[position.second][position.first] = char
73+ }
74+
75+ var last = getStartPosition()
76+ var current = getFirstPipe(last)
77+ var currentChar = getCharAt(current)
78+
79+ while (currentChar != STARTING_CHAR ) {
80+ updateDirectionsMap(
81+ current,
82+ if (verticalPipes.contains(currentChar)) {
83+ if (last == current.add(pipes[currentChar]!! [0 ])) UPWARDS_DIRECTION else DOWNWARDS_DIRECTION
84+ } else OTHER_DIRECTION
85+ )
86+
87+ val newCurrent = current.add(pipes[currentChar]!! .first { current.add(it) != last })
88+ last = current
89+ current = newCurrent
90+ currentChar = getCharAt(current)
91+ }
92+
93+ when (last) {
94+ current.add(pipes[STARTING_CHAR ]!! [0 ]) -> updateDirectionsMap(current, UPWARDS_DIRECTION )
95+ current.add(pipes[STARTING_CHAR ]!! [1 ]) -> updateDirectionsMap(current, DOWNWARDS_DIRECTION )
96+ else -> updateDirectionsMap(current, OTHER_DIRECTION )
97+ }
98+
99+ return directionsMap
100+ }
101+
102+ private fun getStartEndCountCharacters (directionsMap : List <List <Char >>): List <Char > {
103+ directionsMap.forEach { line ->
104+ line.forEach {
105+ if (it != NOT_LOOP )
106+ return listOf ( it, if (it == UPWARDS_DIRECTION ) DOWNWARDS_DIRECTION else UPWARDS_DIRECTION )
107+ }
108+ }
109+ throw NoSuchElementException (" Start and end count characters not found"
110+ }
111+
112+ private fun countTilesEnclosedByLoop (): Int {
113+ val directionsMap = getLoopDirectionsMap()
114+ val (startChar, endChar) = getStartEndCountCharacters(directionsMap)
115+ var counter = 0
116+
117+ directionsMap.forEach { line ->
118+ var shouldCount = false
119+
120+ line.forEach { character ->
121+ if (character == startChar) shouldCount = true
122+ else if (character == endChar) shouldCount = false
123+ else if (shouldCount && character == NOT_LOOP ) counter++
124+ }
125+ }
126+
127+ return counter
128+ }
129+
130+ fun part1 () = println ((getLoopLength() + 1 ) / 2 )
131+
132+ fun part2 () = println (countTilesEnclosedByLoop())
133+ }
134+
135+ fun main () {
136+ Day10 .part1()
137+ Day10 .part2()
138+ }
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