Lösungen für Tag 23, Teil 1

1 files changed, 130 insertions, 0 deletions

diff --git a/src/day23.cpp b/src/day23.cpp
new file mode 100644
index 0000000..6e60e55
--- /dev/null
+++ b/src/day23.cpp
@@ -0,0 +1,130 @@
+#include <algorithm>
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <queue>
+#include <set>
+#include <string>
+#include <vector>
+using namespace std;
+
+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<tuple<size_t, size_t>>
+get_neighbours(const vector<string>& maze, tuple<size_t, size_t> possition)
+{
+        static const tuple<size_t, size_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<tuple<size_t, size_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;
+}
+
+void
+part1(const vector<string>& maze)
+{
+        const tuple<size_t, size_t> start = { 0, maze[0].find('.') };
+        const tuple<size_t, size_t> end   = { maze.size() - 1, maze[maze.size() - 1].find('.') };
+
+        queue<tuple<tuple<size_t, size_t>, set<tuple<size_t, size_t>>>> queue;
+
+        queue.emplace(start, set<tuple<size_t, size_t>>{});
+
+        size_t longest = 0;
+        while ( !queue.empty() ) {
+                auto [position, seen] = queue.front();
+                queue.pop();
+
+                while ( position != end ) {
+                        seen.emplace(position);
+
+                        const auto neighbours = get_neighbours(maze, position);
+
+                        vector<tuple<size_t, size_t>> next_positions;
+
+                        // { neighbours \ seen }
+                        set_difference(neighbours.begin(), neighbours.end(),
+                                       seen.begin(), seen.end(),
+                                       back_inserter(next_positions));
+
+                        if ( next_positions.empty() ) {
+                                break;
+                        }
+
+                        position = next_positions[0];
+
+                        for ( size_t idx = 1; idx != next_positions.size(); ++idx ) {
+                                queue.emplace(next_positions[idx], seen);
+                        }
+                }
+                if ( position == end ) {
+                        longest = max(longest, seen.size());
+                }
+        }
+        cout << longest << endl;
+}
+
+int
+main()
+{
+        const auto maze = read_file("data/day23.txt");
+        part1(maze);
+}