From 8a82c0ed3b119d75778fed7b134fb48fffaceb13 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Thu, 10 Dec 2020 00:18:54 -0500
Subject: [PATCH] Add day 10 part 1 solution

---
 day10/Makefile  | 15 ++++++++++
 day10/day10.cpp | 78 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 day10/Makefile
 create mode 100644 day10/day10.cpp

diff --git a/day10/Makefile b/day10/Makefile
new file mode 100644
index 0000000..4a611cc
--- /dev/null
+++ b/day10/Makefile
@@ -0,0 +1,15 @@
+CC=g++
+BIN_NAME=day10
+CCFLAGS=-o $(BIN_NAME) -g -std=c++17
+LDFLAGS=-lfolly
+
+.PHONY: all, clean
+
+all: $(BIN_NAME)
+
+clean:
+	rm -f $(BIN_NAME)
+
+$(BIN_NAME): day10.cpp
+	$(CC) $(CCFLAGS) $(LDFLAGS) day10.cpp
+
diff --git a/day10/day10.cpp b/day10/day10.cpp
new file mode 100644
index 0000000..cc943d3
--- /dev/null
+++ b/day10/day10.cpp
@@ -0,0 +1,78 @@
+#include <folly/String.h>
+
+#include <algorithm>
+#include <execution>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <regex>
+#include <set>
+#include <string_view>
+#include <vector>
+
+constexpr auto MAX_VOLTAGE_DELTA = 3;
+
+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;
+}
+
+/**
+ * Convert a vector of strings to a vector of numbers
+ * @param input The input for the puzzle
+ * @return std::vector<int> The puzzle input as numbers
+ */
+std::vector<int> convertInputToNumbers(const std::vector<std::string> &input) {
+	std::vector<int> converted;
+	converted.reserve(input.size());
+	std::transform(input.cbegin(), input.cend(), std::back_inserter(converted), [](const std::string &line) {
+		return std::stol(line);
+	});
+
+	return converted;
+}
+
+template <typename Key, typename Value>
+Value getOrDefault(const std::map<Key, Value> &map, Key key, Value defaultValue) {
+	try {
+		return map.at(key);
+	} catch (std::out_of_range) {
+		return defaultValue;
+	}
+}
+
+int part1(const std::vector<int> &input) {
+	std::map<int, int> differenceCounts;
+	std::vector<int> adapters(input);
+	int max_voltage = *std::max_element(input.cbegin(), input.cend()) + MAX_VOLTAGE_DELTA;
+	adapters.insert(adapters.begin(), 0);
+	adapters.insert(adapters.begin(), max_voltage);
+	std::sort(adapters.begin(), adapters.end());
+
+	for (auto it = adapters.cbegin() + 1; it != adapters.cend(); it++) {
+		auto difference = *it - *(it - 1);
+		differenceCounts[difference]++;
+	}
+
+	return getOrDefault(differenceCounts, 1, 0) * getOrDefault(differenceCounts, 3, 0);
+}
+
+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 numericInput = convertInputToNumbers(input);
+
+	std::cout << part1(numericInput) << std::endl;
+	// std::cout << part2(numbers, part1Answer) << std::endl;
+}