diff options
| -rw-r--r-- | README.md | 6 | ||||
| -rw-r--r-- | src/Day03.kt | 46 |
2 files changed, 49 insertions, 3 deletions
@@ -8,9 +8,9 @@ Welcome to the Advent of Code[^aoc] Kotlin project created by [tchojnacki][githu ## Progress | Day | Part 1 | Part 2 | |--------------------|--------|--------| -| Day 1: Sonar Sweep | 🌟 | 🌟 | -| Day 2: Dive! | 🌟 | 🌟 | -| Day 3: ??? | | | +| Day 1: Sonar Sweep | 🌟 | 🌟 | +| Day 2: Dive! | 🌟 | 🌟 | +| Day 3: Binary Diagnostic | 🌟 | 🌟 | | Day 4: ??? | | | | Day 5: ??? | | | | Day 6: ??? | | | diff --git a/src/Day03.kt b/src/Day03.kt new file mode 100644 index 0000000..c6acda4 --- /dev/null +++ b/src/Day03.kt @@ -0,0 +1,46 @@ +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)) +} |