From 7336485d0f3c2f956ca982de2610f5f3f647fadb Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 3 May 2024 15:41:16 +0200
Subject: day 9, advent of code 2022

---
 2022/src/day09.cpp | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 2022/src/day09.cpp

diff --git a/2022/src/day09.cpp b/2022/src/day09.cpp
new file mode 100644
index 0000000..8b99942
--- /dev/null
+++ b/2022/src/day09.cpp
@@ -0,0 +1,116 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <vector>
+using namespace std;
+
+vector<tuple<char, int>>
+read_file(string_view filename)
+{
+	fstream                  input{ filename };
+	vector<tuple<char, int>> result;
+
+	char dir   = 0;
+	int  count = 0;
+
+	while ( input >> dir >> count ) {
+		result.emplace_back(dir, count);
+	}
+
+	return result;
+}
+
+int
+distance(const tuple<int, int>& head, const tuple<int, int>& tail)
+{
+	auto dist_x = abs(get<0>(head) - get<0>(tail));
+	auto dist_y = abs(get<1>(head) - get<1>(tail));
+	return max(dist_x, dist_y);
+};
+
+static map<char, tuple<int, int>> direction = {
+	{ 'R', { +1, 0 } },
+	{ 'L', { -1, 0 } },
+	{ 'U', { 0, +1 } },
+	{ 'D', { 0, -1 } }
+};
+
+void
+part1(const vector<tuple<char, int>>& data)
+{
+	tuple<int, int> head = { 0, 0 };
+	tuple<int, int> tail = head;
+
+	set<tuple<int, int>> positions;
+
+	for ( auto [dir, count]: data ) {
+		while ( count-- > 0 ) {
+			const auto [delta_x, delta_y] = direction[dir];
+			const auto old_head           = head;
+
+			get<0>(head) += delta_x;
+			get<1>(head) += delta_y;
+
+			if ( distance(head, tail) > 1 ) {
+				tail = old_head;
+			}
+
+			positions.insert(tail);
+		}
+	}
+
+	cout << positions.size() << endl;
+}
+
+void
+part2(const vector<tuple<char, int>>& data)
+{
+	static const auto rope_size = 10;
+
+	array<tuple<int, int>, rope_size> rope;
+
+	set<tuple<int, int>> positions;
+
+	for ( auto [dir, count]: data ) {
+		while ( count-- > 0 ) {
+			auto [delta_x, delta_y] = direction[dir];
+
+			get<0>(rope[0]) += delta_x;
+			get<1>(rope[0]) += delta_y;
+
+			for ( size_t i = 1; i < rope.size(); ++i ) {
+				auto& head = rope.at(i - 1);
+				auto& tail = rope.at(i);
+
+				if ( distance(head, tail) > 1 ) {
+					delta_x = get<0>(head) - get<0>(tail);
+					delta_y = get<1>(head) - get<1>(tail);
+
+					if ( abs(delta_x) > 1 ) {
+						delta_x /= abs(delta_x);
+					}
+					if ( abs(delta_y) > 1 ) {
+						delta_y /= abs(delta_y);
+					}
+
+					get<0>(tail) += delta_x;
+					get<1>(tail) += delta_y;
+				}
+			}
+
+			positions.insert(rope[9]);
+		}
+	}
+
+	cout << positions.size() << endl;
+}
+
+int
+main()
+{
+	const auto data = read_file("data/day09.txt");
+	part1(data);
+	part2(data);
+}
-- 
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