From ba8010034e9873cce1a0e20397e69fab460c07ac Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 15 Dec 2024 11:15:46 +0100
Subject: aoc 2024, day 15, part 1

---
 2024/src/day15.cpp | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 2024/src/day15.cpp

(limited to '2024/src')

diff --git a/2024/src/day15.cpp b/2024/src/day15.cpp
new file mode 100644
index 0000000..e11661e
--- /dev/null
+++ b/2024/src/day15.cpp
@@ -0,0 +1,144 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <set>
+#include <string>
+#include <tuple>
+using namespace std;
+
+using pos_type    = tuple<size_t, size_t>;
+using room_type   = set<pos_type>;
+using boxes_type  = set<pos_type>;
+using puzzle_type = tuple<room_type, boxes_type, string, pos_type>;
+
+puzzle_type
+read_file(string_view filename)
+{
+	fstream    input{ filename };
+	room_type  room;
+	boxes_type boxes;
+	string     movements;
+	pos_type   start;
+
+	size_t yPos = 0;
+	for ( string line; getline(input, line); ) {
+		if ( line.empty() ) {
+			continue;
+		}
+
+		if ( line[0] == '#' ) {
+			for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
+				auto chr = line.at(xPos);
+				if ( chr == '#' ) {
+					room.emplace(xPos, yPos);
+				}
+				else if ( chr == 'O' ) {
+					boxes.emplace(xPos, yPos);
+				}
+				else if ( chr == '@' ) {
+					start = { xPos, yPos };
+				}
+			}
+			++yPos;
+		}
+		else {
+			movements += line;
+		}
+	}
+
+	return { room, boxes, movements, start };
+}
+
+void
+print(const room_type& room, const boxes_type& boxes, const pos_type& pos)
+{
+	for ( size_t yPos = 0; yPos != 10; ++yPos ) {
+		for ( size_t xPos = 0; xPos != 10; ++xPos ) {
+			if ( pos == pos_type{ xPos, yPos } ) {
+				cout << '@';
+			}
+			else if ( room.contains({ xPos, yPos }) ) {
+				cout << '#';
+			}
+			else if ( boxes.contains({ xPos, yPos }) ) {
+				cout << 'O';
+			}
+			else {
+				cout << ' ';
+			}
+		}
+		cout << '\n';
+	}
+	cout << endl;
+}
+
+optional<boxes_type>
+can_move(const room_type& room, const boxes_type& boxes, pos_type start, pos_type direction) // NOLINT
+{
+	const auto [x, y]   = start;
+	const auto [dx, dy] = direction;
+
+	boxes_type candidates;
+
+	size_t steps = 1;
+	while ( boxes.contains({ x + dx * steps, y + dy * steps }) ) {
+		candidates.insert({ x + dx * steps, y + dy * steps });
+		++steps;
+	}
+
+	if ( room.contains({ x + dx * steps, y + dy * steps }) ) {
+		return nullopt;
+	}
+
+	return candidates;
+}
+
+void
+part1(const puzzle_type& puzzle)
+{
+	map<char, pos_type> deltas = {
+		{ '<', { -1, 0 } }, // Left
+		{ '^', { 0, -1 } }, // Up
+		{ '>', { 1, 0 } },  // Right
+		{ 'v', { 0, 1 } }   // Down
+	};
+
+	auto [room, boxes, movements, start] = puzzle;
+
+	for ( auto chr: movements ) {
+		const auto delta = deltas[chr];
+		if ( auto bitw = can_move(room, boxes, start, delta) ) {
+			const auto [dx, dy] = delta;
+
+			get<0>(start) += dx;
+			get<1>(start) += dy;
+
+			boxes_type new_boxes;
+			for ( const auto& box: boxes ) {
+				if ( bitw->contains(box) ) {
+					const auto [x, y] = box;
+					new_boxes.emplace(x + dx, y + dy);
+					bitw->erase(box);
+				}
+				else {
+					new_boxes.insert(box);
+				}
+			}
+			boxes = new_boxes;
+		}
+	}
+
+	size_t sum = 0;
+	for (const auto& [x, y]: boxes) {
+		sum += x + 100 * y;
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	const auto data = read_file("data/day15.txt");
+	part1(data);
+}
-- 
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