Day03 2021

2021/src/main/kotlin/Day03.kt

@@ -0,0 +1,37 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.BaseDay
+import be.vandewalleh.aoc.utils.input.Day
+
+@Day
+class Day03 : BaseDay() {
+    override fun part1(): Int {
+        val moreOnes = input.lines.value[0].indices
+            .map { i -> input.lines.value.map { it[i] } }
+            .map { it.count { it == '1' } >= it.size / 2 }
+
+        val gamma = moreOnes.joinToString("") { if (it) "1" else "0" }.toInt(radix = 2)
+        val epsilon = moreOnes.joinToString("") { if (!it) "1" else "0" }.toInt(radix = 2)
+        return gamma * epsilon
+    }
+
+    override fun part2(): Any {
+        val oxygenNumbers = findNumber(input.lines.value) { ones, zeros -> if (ones >= zeros) '1' else '0' }
+        val co2Numbers = findNumber(input.lines.value) { ones, zeros -> if (zeros <= ones) '0' else '1' }
+        return oxygenNumbers[0].toInt(2) * co2Numbers[0].toInt(2)
+    }
+
+    private fun findNumber(input: List<String>, keep: (Int, Int) -> Char): List<String> {
+        var numbers = input
+        for (i in this.input.lines.value[0].indices) {
+            if (numbers.size == 1) break
+            val eachCount = numbers.map { it[i] }.groupingBy { it }.eachCount()
+            val ones = eachCount['1'] ?: 0
+            val zeros = eachCount['0'] ?: 0
+            val maj = keep(ones, zeros)
+            numbers = numbers.filter { it[i] == maj }
+        }
+        return numbers
+    }
+
+}