Add day 5 solution

day5/Makefile

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+CC=g++
+BIN_NAME=day5
+CCFLAGS=-o $(BIN_NAME) -g
+LDFLAGS=-lfolly -std=c++17
+
+.PHONY: all, clean
+
+all: $(BIN_NAME)
+
+clean:
+	rm -f $(BIN_NAME)
+
+$(BIN_NAME): day5.cpp
+	$(CC) $(CCFLAGS) $(LDFLAGS) day5.cpp
+

day5/day5.cpp

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+#include <algorithm>
+#include <execution>
+#include <fstream>
+#include <iostream>
+#include <numeric>
+#include <string_view>
+#include <vector>
+
+// The maximum row of the plane
+constexpr int MAX_ROW = 127;
+constexpr int MAX_COL = 7;
+constexpr char FRONT_CHAR = 'F';
+constexpr char BACK_CHAR = 'B';
+constexpr char RIGHT_CHAR = 'R';
+constexpr char LEFT_CHAR = 'L';
+
+std::vector<std::string> read_input(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;
+}
+
+int getPosFromSpec(std::string_view view, char bottomHalfChar, char topHalfChar, int initMax) {
+	int max = initMax;
+	int min = 0;
+	int stringCursor = 0;
+	for (char candidate : view) {
+		// std::cout << min << " " << max << std::endl;
+		// std::cout << candidate << std::endl;
+		if (candidate == topHalfChar) {
+			max = (max + min) / 2;
+		} else if (candidate == bottomHalfChar) {
+			min += (max - min) / 2 + 1;
+		}
+
+		stringCursor++;
+	}
+
+	return min;
+}
+
+int getColumnSplitPoint(std::string_view view) {
+	int rightPosition = view.find(RIGHT_CHAR);
+	int leftPosition = view.find(LEFT_CHAR);
+	if (rightPosition == std::string_view::npos) {
+		return leftPosition;
+	} else if (leftPosition == std::string_view::npos) {
+		return rightPosition;
+	}
+
+	return std::min(rightPosition, leftPosition);
+}
+
+int parseSeatID(std::string_view view) {
+	int columnSplitPoint = getColumnSplitPoint(view);
+	std::string_view rowSpec = view.substr(0, columnSplitPoint);
+	std::string_view colSpec = view.substr(columnSplitPoint);
+	// std::cout << rowSpec << " " << colSpec << std::endl;
+
+	int rowId = getPosFromSpec(rowSpec, BACK_CHAR, FRONT_CHAR, MAX_ROW);
+	int colId = getPosFromSpec(colSpec, RIGHT_CHAR, LEFT_CHAR, MAX_COL);
+
+	// std::cout << rowId << " " << colId << std::endl;
+	return rowId * (MAX_COL + 1) + colId;
+}
+
+int part1(const std::vector<std::string> &input) {
+	return std::accumulate(input.cbegin(), input.cend(), 0, [](int max, const std::string &row) {
+		int seatId = parseSeatID(row);
+		return std::max(seatId, max);
+	});
+}
+
+int part2(const std::vector<std::string> &input) {
+	std::vector<int> ids;
+	std::transform(input.cbegin(), input.cend(), std::inserter(ids, ids.begin()), [](const std::string &input) {
+		return parseSeatID(input);
+	});
+	std::sort(ids.begin(), ids.end());
+
+	int lastId = ids.at(0);
+	for (auto it = std::next(ids.begin()); it != ids.end(); it++) {
+		if (*it != lastId + 1) {
+			return lastId + 1;
+		}
+		lastId = *it;
+	}
+
+	throw std::invalid_argument("No solution in given input");
+}
+
+int main(int argc, char *argv[]) {
+	if (argc != 2) {
+		std::cerr << argv[0] << " <input_file>" << std::endl;
+		return 1;
+	}
+
+	auto input = read_input(argv[1]);
+	std::cout << part1(input) << std::endl;
+	std::cout << part2(input) << std::endl;
+}