From 75a4f18e6018c9081726fe02ba03863c6028aed1 Mon Sep 17 00:00:00 2001
From: Gnarwhal <git.aspect893@passmail.net>
Date: Wed, 23 Dec 2020 16:35:27 -0800
Subject: [PATCH] Completed day 23

---
 2020/days/day23.cpp | 105 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 2020/days/day23.cpp

diff --git a/2020/days/day23.cpp b/2020/days/day23.cpp
new file mode 100644
index 0000000..f3cc3b4
--- /dev/null
+++ b/2020/days/day23.cpp
@@ -0,0 +1,105 @@
+/*******************************************************************************
+ *
+ * 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 <array>
+#include <string>
+#include <iostream>
+#include <fstream>
+
+#include "../misc/types.hpp"
+#include "../misc/print.hpp"
+
+constexpr auto CUP_COUNT = 9;
+
+auto day23() -> void {
+	auto start = usize(0);
+	auto nums = std::array<usize, CUP_COUNT>();
+	auto big_nums = std::vector<usize>(1000000);
+	{
+		auto line = std::string();
+		auto file = std::ifstream("inputs/day23.input");
+		getline(file, line);
+		for (auto i = usize(0); i < CUP_COUNT; ++i) {
+			nums[line[i] - '1'] = line[(i + 1) % CUP_COUNT] - '1';
+		}
+		start = line[0] - '1';
+		for (auto i = usize(0); i < CUP_COUNT; ++i) {
+			if (nums[i] != start) {
+				big_nums[i] = nums[i];
+			} else {
+				big_nums[i] = CUP_COUNT;
+			}
+		}
+		for (auto i = CUP_COUNT; i < big_nums.size() - 1; ++i) {
+			big_nums[i] = i + 1;
+		}
+		big_nums[big_nums.size() - 1] = start;
+	}
+
+	auto begin = usize(0);
+	auto end   = usize(0);
+
+	// Part 1
+	auto current = start;
+	for (auto i = usize(0); i < 100; ++i) {
+		begin = nums[current];
+		end   = nums[nums[begin]];
+		nums[current] = nums[end];
+		auto destination = current;
+		while (
+			   begin       == (destination = (destination + CUP_COUNT - 1) % CUP_COUNT)
+			|| nums[begin] ==  destination
+			|| end         ==  destination
+		);
+		nums[end] = nums[destination];
+		nums[destination] = begin;
+		current = nums[current];
+	}
+	auto out = std::array<c8, CUP_COUNT + 1>{ 0 };
+	for (auto i = nums[0], j = usize(0); i != 0; i = nums[i], ++j) {
+		out[j] = (i + '1');
+	}
+	print(&out[0]);
+
+	// Part 2
+	current = start;
+	for (auto i = usize(0); i < 10000000; ++i) {
+		begin = big_nums[current];
+		end   = big_nums[big_nums[begin]];
+		big_nums[current] = big_nums[end];
+		auto destination = current;
+		while (
+			   begin           == (destination = (destination + big_nums.size() - 1) % big_nums.size())
+			|| big_nums[begin] ==  destination
+			|| end             ==  destination
+		);
+		big_nums[end] = big_nums[destination];
+		big_nums[destination] = begin;
+		current = big_nums[current];
+	}
+	print(((big_nums[0] + 1) * (big_nums[big_nums[0]] + 1)));
+}