From 756f22d58bb198b8f34589c112e1003614ccdcd6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 2 Nov 2025 21:41:58 +0100
Subject: aoc 2017, days 1-20

---
 2017/src/day03.cpp | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 2017/src/day03.cpp

(limited to '2017/src/day03.cpp')

diff --git a/2017/src/day03.cpp b/2017/src/day03.cpp
new file mode 100644
index 0000000..417cef3
--- /dev/null
+++ b/2017/src/day03.cpp
@@ -0,0 +1,94 @@
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <iostream>
+#include <map>
+
+using namespace std;
+
+namespace {
+
+void
+part1(int value)
+{
+	auto ring      = static_cast<int>(ceil((sqrt(value) - 1) / 2));
+	auto side_len  = (2 * ring) + 1;
+	auto max_value = side_len * side_len;
+
+	array<int, 4> centers = {
+		max_value - ring - (2 * ring * 0),
+		max_value - ring - (2 * ring * 1),
+		max_value - ring - (2 * ring * 2),
+		max_value - ring - (2 * ring * 3)
+	};
+
+	auto* itr = ranges::min_element(centers, {}, [value](int rhs) { return abs(value - rhs); });
+
+	auto dist_to_center = abs(value - *itr);
+
+	cout << "Part1: " << ring + dist_to_center << '\n';
+}
+
+void
+part2(int value)
+{
+	static const array<tuple<int, int>, 4> dirs{
+		make_tuple(1, 0),  // right
+		make_tuple(0, -1), // up
+		make_tuple(-1, 0), // left
+		make_tuple(0, 1),  // down
+	};
+
+	static const array<int, 3> offsets = { -1, 0, 1 };
+
+	map<tuple<int, int>, int> grid; // (x,y) => value
+
+	int x     = 0;
+	int y     = 0;
+	int steps = 1;
+
+	grid[{ x, y }] = 1;
+
+	while ( true ) {
+		for ( const auto [dx, dy]: dirs ) {
+			for ( int _ = 0; _ != steps; ++_ ) {
+				x += dx;
+				y += dy;
+
+				int sum = 0;
+				for ( const auto off_x: offsets ) {
+					for ( const auto off_y: offsets ) {
+						if ( off_x == 0 && off_y == 0 ) {
+							continue;
+						}
+
+						const auto pos = make_tuple(x + off_x, y + off_y);
+						if ( grid.contains(pos) ) {
+							sum += grid.at(pos);
+						}
+					}
+				}
+
+				if ( sum > value ) {
+					cout << "Part2: " << sum << '\n';
+					return;
+				}
+
+				grid[{ x, y }] = sum;
+			}
+			if ( dx == 0 ) {
+				++steps;
+			}
+		}
+	}
+}
+
+} // namespace
+
+int
+main()
+{
+	static const auto puzzle = 265149;
+	part1(puzzle);
+	part2(puzzle);
+}
-- 
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