From 5f92ea475dadc173b2172834227f9392fd7d5a7c Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 10 Jan 2025 19:34:39 +0100
Subject: aoc 2016, day 1

---
 2016/src/day01.cpp | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 2016/src/day01.cpp

(limited to '2016/src')

diff --git a/2016/src/day01.cpp b/2016/src/day01.cpp
new file mode 100644
index 0000000..f5d74a5
--- /dev/null
+++ b/2016/src/day01.cpp
@@ -0,0 +1,122 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+split(string_view line, string_view delimiter)
+{
+	size_t pos_start = 0;
+	size_t pos_end   = 0;
+
+	vector<string> res;
+
+	while ( (pos_end = line.find(delimiter, pos_start)) != string::npos ) {
+		auto token = line.substr(pos_start, pos_end - pos_start);
+		pos_start  = pos_end + delimiter.length();
+
+		res.emplace_back(token);
+	}
+
+	if ( pos_start != line.size() ) {
+		res.emplace_back(line.substr(pos_start));
+	}
+	return res;
+}
+
+vector<tuple<char, long>>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+	string  content{ istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
+
+	vector<tuple<char, long>> result;
+	for ( const auto& part: split(content, ", ") ) {
+		result.emplace_back(part[0], stol(part.substr(1)));
+	}
+	return result;
+}
+
+void
+part1(const vector<tuple<char, long>>& input)
+{
+	array<tuple<long, long>, 4> dirs = {
+		make_tuple(1L, 0L),
+		make_tuple(0L, 1L),
+		make_tuple(-1L, 0L),
+		make_tuple(0L, -1L)
+	};
+
+	size_t dir   = 0;
+	long   pos_x = 0;
+	long   pos_y = 0;
+
+	for ( const auto& [change, length]: input ) {
+		if ( change == 'L' ) {
+			dir = (dir + 1) % 4;
+		}
+		else {
+			dir = (dir + 3) % 4;
+		}
+
+		auto [delta_x, delta_y] = dirs.at(dir);
+
+		pos_x += length * delta_x;
+		pos_y += length * delta_y;
+	}
+
+	cout << abs(pos_x) + abs(pos_y) << endl;
+}
+
+void
+part2(const vector<tuple<char, long>>& input)
+{
+	array<tuple<long, long>, 4> dirs = {
+		make_tuple(1L, 0L),
+		make_tuple(0L, 1L),
+		make_tuple(-1L, 0L),
+		make_tuple(0L, -1L)
+	};
+
+	size_t dir   = 0;
+	long   pos_x = 0;
+	long   pos_y = 0;
+
+	set<tuple<long, long>> visited;
+
+	for ( auto [change, length]: input ) {
+		if ( change == 'L' ) {
+			dir = (dir + 1) % 4;
+		}
+		else {
+			dir = (dir + 3) % 4;
+		}
+
+		auto [delta_x, delta_y] = dirs.at(dir);
+
+		while ( length-- > 0 ) {
+			pos_x += delta_x;
+			pos_y += delta_y;
+
+			if ( visited.contains({ pos_x, pos_y }) ) {
+				cout << abs(pos_x) + abs(pos_y) << endl;
+				return;
+			}
+
+			visited.emplace(pos_x, pos_y);
+		}
+	}
+}
+
+int
+main()
+{
+	auto input = read_file("data/day01.txt");
+	part1(input);
+	part2(input);
+}
-- 
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