1 files changed, 205 insertions, 11 deletions

diff --git a/2024/src/day15.cpp b/2024/src/day15.cpp
index 5c2449b..94b8a2b 100644
--- a/2024/src/day15.cpp
+++ b/2024/src/day15.cpp
@@ -1,3 +1,4 @@
+#include <cassert>
 #include <fstream>
 #include <iostream>
 #include <map>
@@ -8,10 +9,12 @@
 #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>;
+using pos_type     = tuple<size_t, size_t>;
+using room_type    = set<pos_type>;
+using boxes_type   = set<pos_type>;
+using boxes2_type  = map<pos_type, bool>;
+using puzzle_type  = tuple<room_type, boxes_type, string, pos_type>;
+using puzzle2_type = tuple<room_type, boxes2_type, string, pos_type>;
 
 puzzle_type
 read_file(string_view filename)
@@ -51,12 +54,59 @@ read_file(string_view filename)
         return { room, boxes, movements, start };
 }
 
-/*
+puzzle2_type
+read_file2(string_view filename)
+{
+        fstream     input{ filename };
+        room_type   room;
+        boxes2_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 * 2, yPos);
+                                        room.emplace(xPos * 2 + 1, yPos);
+                                }
+                                else if ( chr == 'O' ) {
+                                        boxes.insert({ pos_type(xPos * 2, yPos), true });
+                                        boxes.insert({ pos_type(xPos * 2 + 1, yPos), false });
+                                }
+                                else if ( chr == '@' ) {
+                                        start = { xPos * 2, 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 ) {
+        size_t width  = 0;
+        size_t height = 0;
+
+        for ( const auto& [x, y]: room ) {
+                width  = max(width, x + 1);
+                height = max(height, y + 1);
+        }
+
+        for ( size_t yPos = 0; yPos != height; ++yPos ) {
+                for ( size_t xPos = 0; xPos != width; ++xPos ) {
                         if ( pos == pos_type{ xPos, yPos } ) {
                                 cout << '@';
                         }
@@ -67,14 +117,45 @@ print(const room_type& room, const boxes_type& boxes, const pos_type& pos)
                                 cout << 'O';
                         }
                         else {
-                                cout << ' ';
+                                cout << '.';
+                        }
+                }
+                cout << '\n';
+        }
+        cout << endl;
+}
+
+void
+print(const room_type& room, const boxes2_type& boxes, const pos_type& pos)
+{
+        size_t width  = 0;
+        size_t height = 0;
+
+        for ( const auto& [x, y]: room ) {
+                width  = max(width, x + 1);
+                height = max(height, y + 1);
+        }
+
+        for ( size_t yPos = 0; yPos != height; ++yPos ) {
+                for ( size_t xPos = 0; xPos != width; ++xPos ) {
+                        if ( pos == pos_type{ xPos, yPos } ) {
+                                cout << '@';
+                        }
+                        else if ( room.contains({ xPos, yPos }) ) {
+                                cout << '#';
+                        }
+                        else if ( boxes.contains({ xPos, yPos }) ) {
+                                auto value = boxes.at({ xPos, yPos });
+                                cout << (value ? '[' : ']');
+                        }
+                        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
@@ -132,9 +213,122 @@ part1(const puzzle_type& puzzle)
         }) << endl;
 }
 
+tuple<pos_type, pos_type>
+get_both_parts(const boxes2_type& boxes, pos_type pos)
+{
+        const auto [x, y] = pos;
+        if ( boxes.at(pos) ) {
+                return { pos, { x + 1, y } };
+        }
+        else {
+                return { { x - 1, y }, pos };
+        }
+}
+
+optional<boxes2_type>
+can_move(const room_type& room, const boxes2_type& all_boxes, pos_type start, pos_type direction) // NOLINT
+{
+        function<optional<boxes2_type>(const boxes2_type&, size_t)> can_move_up_down = [&room, &all_boxes, &can_move_up_down](const boxes2_type& boxes, size_t dy) -> optional<boxes2_type> {
+                boxes2_type candidates;
+
+                for ( const auto& [pos, b]: boxes ) {
+                        const auto [x, y] = pos;
+                        pos_type try_pos(x, y + dy);
+
+                        if ( room.contains(try_pos) ) {
+                                return nullopt;
+                        }
+
+                        if ( all_boxes.contains(try_pos) ) {
+                                const auto [lhs, rhs] = get_both_parts(all_boxes, try_pos);
+
+                                assert(all_boxes.contains(lhs) && all_boxes.at(lhs) == true);  // NOLINT
+                                assert(all_boxes.contains(rhs) && all_boxes.at(rhs) == false); // NOLINT
+
+                                candidates.emplace(lhs, true);
+                                candidates.emplace(rhs, false);
+                        }
+                }
+
+                if ( candidates.empty() ) {
+                        return boxes2_type{};
+                }
+
+                if ( auto results = can_move_up_down(candidates, dy) ) {
+                        for ( const auto& result: results.value() ) {
+                                candidates.insert(result);
+                        }
+                        return candidates;
+                }
+
+                return nullopt;
+        };
+
+        const auto [x, y]   = start;
+        const auto [dx, dy] = direction;
+
+        if ( dy != 0 ) {
+                return can_move_up_down({ { start, false } }, dy);
+        }
+
+        boxes2_type candidates;
+
+        size_t steps = 1;
+        while ( all_boxes.contains({ x + dx * steps, y + dy * steps }) ) {
+                auto foo = all_boxes.at({ x + dx * steps, y + dy * steps });
+                candidates.insert({ { x + dx * steps, y + dy * steps }, foo });
+                ++steps;
+        }
+
+        if ( room.contains({ x + dx * steps, y + dy * steps }) ) {
+                return nullopt;
+        }
+
+        return candidates;
+}
+
+void
+part2(const puzzle2_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;
+
+                        for ( const auto& [box, b]: bitw.value() ) {
+                                boxes.erase(box);
+                        }
+
+                        for ( auto [pos, b]: bitw.value() ) {
+                                const auto [x, y] = pos;
+                                boxes.emplace(pos_type{ x + dx, y + dy }, b);
+                        }
+                }
+        }
+
+        cout << accumulate(boxes.begin(), boxes.end(), 0UL, [](auto init, const auto& box) {
+                const auto& [pos, b] = box;
+                if ( !b ) {
+                        return init;
+                }
+                return init + get<0>(pos) + 100 * get<1>(pos);
+        }) << endl;
+}
 int
 main()
 {
-        const auto data = read_file("data/day15.txt");
-        part1(data);
+        part1(read_file("data/day15.txt"));
+        part2(read_file2("data/day15.txt"));
 }