Completed day 13 p1 and day 14

2020/days/day13.cpp

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+/*******************************************************************************
+ *
+ * Copyright (c) 2020 Gnarwhal
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files(the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ *******************************************************************************/
+
+#include <vector>
+#include <string>
+#include <iostream>
+#include <fstream>
+
+#include "../misc/types.hpp"
+#include "../misc/print.hpp"
+
+struct Pair{ u64 id; usize index; };
+
+auto find_least(u64 new_base, u64 new_loop, u64 req_base, u64 req_loop, u64 iter) -> u64 {
+	while ((new_base + ++iter * new_loop - req_base) % req_loop != 0);
+	return new_base + iter * new_loop;
+}
+
+auto day13() -> void {
+	auto ready = usize(0);
+	auto buses = std::vector<Pair>();
+	{
+		auto line = std::string();
+		auto file = std::ifstream("inputs/day13.input");
+		getline(file, line);
+		ready = std::stoi(line);
+		getline(file, line);
+		auto start = usize(0);
+		auto end   = usize(0);
+		auto index = usize(0);
+		auto id    = std::string();
+		while ((end = line.find(',', start)) != std::string::npos) {
+			id = line.substr(start, end - start);
+			if (id != "x") {
+				buses.push_back({ u64(std::stoi(line.substr(start, end - start))), index });
+			}
+			start = end + 1;
+			++index;
+		}
+		end = line.size();
+		id = line.substr(start, end - start);
+		if (id != "x") {
+			buses.push_back({ u64(std::stoi(line.substr(start, end - start))), index });
+		}
+	}
+	
+	auto id      = buses[0].id;
+	auto minutes = buses[0].id - (ready % buses[0].id);
+	for (auto i = usize(1); i < buses.size(); ++i) {
+		auto local_minutes = buses[i].id - (ready % buses[i].id);
+		if (local_minutes < minutes) {
+			id      = buses[i].id;
+			minutes = local_minutes;
+		}
+	}
+	print((id * minutes));
+
+	auto req_base = usize(0);
+	auto req_loop = usize(1);
+	for (auto i = usize(1); i < buses.size(); ++i) {
+		auto base_loop = usize(-1);
+		while ((++base_loop * buses[0].id + buses[i].index) % buses[i].id != 0);
+
+		auto rep_loop = usize(0);
+		while ((++rep_loop * buses[0].id) % buses[i].id != 0);
+
+		req_base = find_least(base_loop, rep_loop, req_base, req_loop, -1);
+		if (i < buses.size() - 1) {
+			req_loop = find_least(0, rep_loop, 0, req_loop, 0);
+		}
+		/*
+		required_base (rqb), required_loop (rql)
+
+		base_loop (bl), repeat_loop (rl)
+
+		rqb + a0 * rql = bl + a1 * rl < minimize and store in required loop
+		a0 = (bl + a1 * rl - rqb) / rql
+
+		b0 * rql = b1 * rl < minimize and store in required loop
+		*/
+	}
+	print((req_base * buses[0].id));
+}