2018/src/day01.cpp


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#include <filesystem>
#include <fstream>
#include <iostream>
#include <numeric>
#include <unordered_set>
#include <vector>

using namespace std;

namespace {

vector<long>
read_file(const filesystem::path& filename)
{
	ifstream     file{ filename };
	vector<long> values;

	for ( long value = 0; file >> value; ) {
		values.emplace_back(value);
	}

	return values;
}

void
part1(const vector<long>& values)
{
	auto sum = accumulate(values.begin(), values.end(), 0L);
	cout << "Part1: " << sum << '\n';
}

void
part2(const vector<long>& values)
{
	unordered_set<long> seen;

	long sum = 0;
	for ( size_t idx = 0;; ++idx ) {
		sum += values.at(idx % values.size());

		if ( seen.contains(sum) ) {
			cout << "Part2: " << sum << '\n';
			return;
		}

		seen.emplace(sum);
	}
}

} // namespace

int
main()
{
	auto values = read_file("data/day01.txt");
	part1(values);
	part2(values);
}