advent_of_code/2020/days/day10.cpp

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#include <vector>
#include <string>
#include <iostream>
#include <fstream>

#include "../misc/types.hpp"
#include "../misc/print.hpp"

struct Pair {
	u64 jolt;
	u64 count;
};

auto operator<(const Pair & left, const Pair & right) -> bool {
	return left.jolt < right.jolt;
}

auto day10() -> void {
	auto jolts = std::vector<Pair>{{ 0, 1 }};
	{
		auto line = std::string();
		auto file = std::ifstream("inputs/day10.input");
		while (getline(file, line)) {
			jolts.push_back({ (u64) std::stoll(line), 0 });
		}
	}
	std::sort(jolts.begin(), jolts.end());
	jolts.push_back({ jolts[jolts.size() - 1].jolt + 3, 0 });

	auto dif1 = usize(0);
	auto dif3 = usize(0);
	for (auto i = usize(0); i < jolts.size() - 1; ++i) {
		     if (jolts[i + 1].jolt - jolts[i].jolt == 1) ++dif1;
		else if (jolts[i + 1].jolt - jolts[i].jolt == 3) ++dif3;
	}

	print((dif1 * dif3));

	for (auto i = i32(0); i < jolts.size() - 1; ++i) {
		for (auto j = i + 1; j < jolts.size(); ++j) {
			if (jolts[j].jolt <= jolts[i].jolt + 3) {
				jolts[j].count += jolts[i].count;
			} else {
				break;
			}
		}
	}
	print(jolts[jolts.size() - 1].count);
}