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fun main() {
fun addLists(l1: List<Int>, l2: List<Int>): List<Int> = l1.zip(l2).map { it.first + it.second }
fun bitListToNumber(bitList: List<Int>): Int = bitList.reduce { acc, bit -> acc * 2 + bit }
fun binaryStringToBitList(binaryString: String): List<Int> = binaryString.toList().map { bit -> bit.toString().toInt() }
fun mostCommonBits(input: List<List<Int>>): List<Int> =
input
.reduce(::addLists)
.map { bit -> if (bit.toDouble() / input.size >= 0.5) { 1 } else { 0 } }
fun part1(input: List<String>): Int =
mostCommonBits(input.map(::binaryStringToBitList))
.let { gammaBits ->
val epsilonBits = gammaBits.map { bit -> 1 - bit }
return bitListToNumber(gammaBits) * bitListToNumber(epsilonBits)
}
fun part2(input: List<String>): Int {
var oxygenList = input.map(::binaryStringToBitList)
var oxygenIdx = 0
while (oxygenList.size > 1) {
oxygenList = oxygenList.filter { e -> e[oxygenIdx] == mostCommonBits(oxygenList)[oxygenIdx]}
oxygenIdx += 1
}
var scrubberList = input.map(::binaryStringToBitList)
var scrubberIdx = 0
while (scrubberList.size > 1) {
scrubberList = scrubberList.filter { e -> e[scrubberIdx] != mostCommonBits(scrubberList)[scrubberIdx]}
scrubberIdx += 1
}
return bitListToNumber(oxygenList[0]) * bitListToNumber(scrubberList[0])
}
val testInput = readInput("Day03_test")
check(part1(testInput) == 198)
check(part2(testInput) == 230)
val input = readInput("Day03")
println(part1(input))
println(part2(input))
}
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