Add day1 solution

day1/day1.cpp

@@ -0,0 +1,71 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <set>
+
+constexpr int TARGET_NUM = 2020;
+
+/**
+ * Read the input and get it as a set of integers
+ * @param filename The filename to read from
+ * @return std::set<int> A set of the numbers in the input
+ */
+std::set<int> read_input(const std::string &filename)
+{
+	std::set<int> input;
+	std::string line;
+	std::ifstream file(filename);
+
+	while (std::getline(file, line))
+	{
+		int num = std::stoi(line);
+		input.insert(num);
+	}
+
+	return input;
+}
+
+int part1(const std::set<int> &inputs)
+{
+	for (int num : inputs)
+	{
+		int desired = TARGET_NUM - num;
+		if (inputs.find(desired) != inputs.end())
+		{
+			return desired * num;
+		}
+	}
+
+	throw "Does not contain solution";
+}
+
+int part2(const std::set<int> &inputs)
+{
+	for (int num : inputs)
+	{
+		for (int num2 : inputs)
+		{
+			int desired = TARGET_NUM - (num + num2);
+			if (inputs.find(desired) != inputs.end())
+			{
+				return desired * num2 * num;
+			}
+		}
+	}
+
+	throw std::runtime_error("Does not contain solution");
+}
+
+int main(int argc, const char *argv[])
+{
+	if (argc != 2)
+	{
+		std::cerr << "./day1 <input_file>" << std::endl;
+		return 1;
+	}
+
+	std::set<int> inputs = read_input(argv[1]);
+	std::cout << part1(inputs) << std::endl;
+	std::cout << part2(inputs) << std::endl;
+}