Prepare for other years

2020-12-30 18:01:52 +01:00
parent 522618d106
commit 4a90257257
81 changed files with 277 additions and 253 deletions
@@ -0,0 +1,49 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import kotlin.math.abs
+
+private data class Bus(val index: Int, val id: Long)
+
+@Day(13)
+class Day13(@Lines val input: Input<List<String>>) {
+
+    fun part1(): Int {
+        val id = input.value[0].toInt()
+
+        val (busId, min) = input.value[1]
+            .splitToSequence(",")
+            .filterNot { it == "x" }
+            .map { it.toInt() }
+            .map { bus -> bus to id / bus }
+            .map { (bus, div) -> bus to bus * (div + 1) }
+            .minByOrNull { it.second }!!
+
+        return busId * abs(min - id)
+    }
+
+    private tailrec fun gcd(a: Long, b: Long): Long = if (b == 0L) a else gcd(b, a % b)
+    private fun lcm(a: Long, b: Long): Long = a / gcd(a, b) * b
+
+    fun part2(): Long {
+        val buses = input.value[1]
+            .splitToSequence(",")
+            .mapIndexedNotNull { index, bus ->
+                if (bus == "x") null
+                else Bus(index, bus.toLong())
+            }
+            .toList()
+
+        var step = 1L
+        var t = 0L
+
+        for ((i, id) in buses) {
+            while ((t + i) % id != 0L) t += step
+            step = lcm(step, id)
+        }
+
+        return t
+    }
+}