From 56e890cec0a28c0a485212ccebfaf774235a79a2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 3 Jan 2024 23:35:54 +0100
Subject: prepare for more puzzles ... :)

---
 2023/src/day23.cpp | 152 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 2023/src/day23.cpp

(limited to '2023/src/day23.cpp')

diff --git a/2023/src/day23.cpp b/2023/src/day23.cpp
new file mode 100644
index 0000000..d8c20d3
--- /dev/null
+++ b/2023/src/day23.cpp
@@ -0,0 +1,152 @@
+#include <algorithm>
+#include <array>
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <iterator>
+#include <map>
+#include <queue>
+#include <set>
+#include <string>
+#include <vector>
+using namespace std;
+
+using position_t = tuple<size_t, size_t>;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+set<position_t>
+get_neighbours(const vector<string>& maze, position_t possition)
+{
+	static const position_t deltas[] = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } }; // NOLINT
+
+	static const auto SYM_UP    = '^';
+	static const auto SYM_RIGHT = '>';
+	static const auto SYM_DOWN  = 'v';
+	static const auto SYM_LEFT  = '<';
+
+	const auto [row, col] = possition;
+
+	switch ( maze[row][col] ) {
+	case SYM_UP:
+		return { make_tuple(row - 1, col) };
+	case SYM_RIGHT:
+		return { make_tuple(row, col + 1) };
+	case SYM_DOWN:
+		return { make_tuple(row + 1, col) };
+	case SYM_LEFT:
+		return { make_tuple(row, col - 1) };
+	}
+
+	set<position_t> positions;
+
+	for ( const auto& delta: deltas ) {
+		const auto new_row = row + get<0>(delta);
+		const auto new_col = col + get<1>(delta);
+
+		if ( new_row >= maze.size() || new_col >= maze[0].size() ) {
+			continue;
+		}
+
+		if ( maze[new_row][new_col] == '#' ) {
+			continue;
+		}
+
+		if ( new_row < row && maze[new_row][new_col] == SYM_DOWN ) {
+			continue;
+		}
+		if ( new_row > row && maze[new_row][new_col] == SYM_UP ) {
+			continue;
+		}
+		if ( new_col < col && maze[new_row][new_col] == SYM_RIGHT ) {
+			continue;
+		}
+		if ( new_col > col && maze[new_row][new_col] == SYM_LEFT ) {
+			continue;
+		}
+
+		positions.emplace(new_row, new_col);
+	}
+
+	return positions;
+}
+
+set<position_t>
+get_neighbours2(const vector<string>& maze, position_t possition)
+{
+	static const position_t deltas[] = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } }; // NOLINT
+
+	const auto [row, col] = possition;
+
+	set<position_t> positions;
+
+	for ( const auto& delta: deltas ) {
+		const auto new_row = row + get<0>(delta);
+		const auto new_col = col + get<1>(delta);
+
+		if ( new_row >= maze.size() || new_col >= maze[0].size() ) {
+			continue;
+		}
+
+		if ( maze[new_row][new_col] == '#' ) {
+			continue;
+		}
+
+		positions.emplace(new_row, new_col);
+	}
+
+	return positions;
+}
+
+void
+solve(const vector<string>& maze, function<set<position_t>(const vector<string>&, position_t)> neighbours)
+{
+	const position_t start = { 0, maze[0].find('.') };
+	const position_t end   = { maze.size() - 1, maze[maze.size() - 1].find('.') };
+
+	vector<vector<bool>> visited(maze.size(), vector<bool>(maze[0].size()));
+
+	function<long(position_t, long)> find_longest_path = [&](position_t position, long current) -> long {
+		const auto [row, col] = position;
+
+		if ( visited[row][col] ) {
+			return 0;
+		}
+
+		if ( position == end ) {
+			return current;
+		}
+
+		long value = 0;
+
+		visited[row][col] = true;
+		for ( const auto& neighbour: neighbours(maze, position) ) {
+			value = max(value, find_longest_path(neighbour, current + 1));
+		}
+		visited[row][col] = false;
+
+		return value;
+	};
+
+	auto value = find_longest_path(start, 0);
+	cout << value << endl;
+}
+
+int
+main()
+{
+	const auto maze = read_file("data/day23.txt");
+	solve(maze, get_neighbours);
+	solve(maze, get_neighbours2);
+}
-- 
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