advent-of-code/2023/8/main-2.cpp

#include <bits/stdc++.h>
using namespace std;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	string instructions;
	getline(cin, instructions);
	cin.ignore(1);

	unordered_map<string, pair<string, string>> locs;

	string line;
	while (getline(cin, line)) {
		locs[line.substr(0, 3)] = make_pair(line.substr(7, 3), line.substr(12, 3));
	}

	vector<string> starts;

	for (auto& loc : locs) {
		if (loc.first[2] == 'A')
			starts.push_back(loc.first);
	}

	unsigned long amounts[starts.size()];
	memset(amounts, 0, starts.size() * sizeof(unsigned long));

	long n = 0;
	unsigned int done = starts.size();
	while (done > 0) {
		for (unsigned int i = 0; i < starts.size(); i++) {
			if (amounts[i] != 0)
				continue;

			if (instructions[n % instructions.length()] == 'L')
				starts[i] = locs[starts[i]].first;
			else
				starts[i] = locs[starts[i]].second;
			if (starts[i][2] == 'Z') {
				amounts[i] = n + 1;
				done--;
			}
		}
		n++;
	}

	unsigned long val = amounts[0];
	for (unsigned int i = 1; i < starts.size(); i++) {
		val = lcm(val, amounts[i]);
	}

	cout << val << '\n';
}