Move year 2021 into a subfolder

1 files changed, 51 insertions, 0 deletions

diff --git a/2021-kotlin/src/Day08.kt b/2021-kotlin/src/Day08.kt
new file mode 100644
index 0000000..b513352
--- /dev/null
+++ b/2021-kotlin/src/Day08.kt
@@ -0,0 +1,51 @@
+object Day08 {
+    fun part1(input: List<String>): Int =
+        input.sumOf {
+            it
+                .split("|")[1]
+                .trim()
+                .split(" ")
+                .map(String::length)
+                .count { len -> len in listOf(2, 3, 4, 7) }
+        }
+
+    fun part2(input: List<String>): Long = input.sumOf { line ->
+        val (patternString, outputString) = line.split("|").map(String::trim)
+        val patterns = patternString.split(" ").map(String::toSet)
+
+        val one = patterns.first { it.size == 2 }
+        val four = patterns.first { it.size == 4 }
+        val seven = patterns.first { it.size == 3 }
+        val eight = patterns.first { it.size == 7 }
+
+        val top = seven - one
+        val middle = patterns.filter { it.size == 5 }.reduce(Set<Char>::intersect) intersect four
+        val five = patterns.filter { it.size == 6 }.reduce(Set<Char>::intersect) + middle
+        val bottom = five - (four + top)
+        val nine = four + top + bottom
+        val lowerLeft = eight - nine
+        val six = five + lowerLeft
+        val lowerRight = one intersect six
+        val three = one + top + middle + bottom
+        val zero = eight - middle
+        val upperLeft = nine - three
+        val two = eight - (upperLeft + lowerRight)
+
+        val encodings = listOf(zero, one, two, three, four, five, six, seven, eight, nine)
+
+        outputString
+            .split(" ")
+            .joinToString("") { encodings.indexOf(it.toSet()).toString() }
+            .toLong()
+    }
+}
+
+fun main() {
+    val testInput = readInputAsLines("Day08_test")
+    check(Day08.part1(testInput) == 26)
+    check(Day08.part2(testInput) == 61229L)
+
+    val input = readInputAsLines("Day08")
+    println(Day08.part1(input))
+    println(Day08.part2(input))
+}