Add messy day 13 part 1 solution

day13/day13.cpp

@@ -0,0 +1,78 @@
+#include <folly/String.h>
+
+#include <algorithm>
+#include <charconv>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <vector>
+
+constexpr auto OUT_OF_SERVICE_BUS = "x";
+
+std::vector<std::string> readInput(const std::string &filename) {
+	std::vector<std::string> input;
+	std::string line;
+	std::ifstream file(filename);
+	while (std::getline(file, line)) {
+		input.push_back(line);
+	}
+
+	return input;
+}
+
+std::pair<int, std::vector<std::string>> splitInput(const std::vector<std::string> &input) {
+	int startTime = std::stoi(input.at(0));
+	const std::string &rawBusses = input.at(1);
+	std::vector<std::string> rawBusTimes;
+	folly::split(",", rawBusses, rawBusTimes);
+
+	return std::pair<int, std::vector<std::string>>(startTime, rawBusTimes);
+}
+
+int part1(int busStartTime, const std::vector<std::string> &rawBusTimes) {
+	std::vector<int> busTimes;
+	busTimes.reserve(rawBusTimes.size());
+	for (const std::string &rawBusTime : rawBusTimes) {
+		if (rawBusTime == OUT_OF_SERVICE_BUS) {
+			continue;
+		}
+
+		int busTime = std::stoi(rawBusTime);
+		busTimes.push_back(busTime);
+	}
+
+	// Calculate the bus times that are immediately after the start time input
+	std::map<int, int> nextBusses;
+	std::transform(
+		busTimes.cbegin(), busTimes.cend(), std::inserter(nextBusses, nextBusses.end()), [busStartTime](int busTime) {
+			// Take the ceiling when dividing
+			int numIntervals = (busTime + busStartTime - 1) / busTime;
+			int nextBusTime = busTime * numIntervals;
+
+			return std::pair<int, int>(busTime, nextBusTime);
+		});
+
+	auto minPairIterator = std::min_element(
+		nextBusses.cbegin(), nextBusses.cend(), [](std::pair<int, int> time1, std::pair<int, int> time2) {
+			return time1.second < time2.second;
+		});
+
+	int bestBusID = minPairIterator->first;
+	int bestBusTime = minPairIterator->second;
+	int timeToWait = bestBusTime - busStartTime;
+
+	return bestBusID * timeToWait;
+}
+
+int main(int argc, char *argv[]) {
+	if (argc != 2) {
+		std::cerr << argv[0] << " <input_file>" << std::endl;
+		return 1;
+	}
+
+	auto input = readInput(argv[1]);
+	auto parsedInput = splitInput(input);
+
+	std::cout << part1(parsedInput.first, parsedInput.second) << std::endl;
+}