Day 6

d06/main.cxx

@@ -1,15 +1,220 @@
 #include <iostream>
-#include <fstream>
+#include <sstream>
+#include <string>
+#include <vector>
+#include <chrono>
+#include <algorithm>
+#include <ranges> 
+#include <unordered_set>
 
 using std::cout, std::endl;
 
-int main() {
-    std::ifstream file{"../d6/input.txt"};
-    std::string line;
+constexpr const char content[] = {
+    #embed "input.txt"
+};
 
-    while (std::getline(file, line)) {
-        
+enum Direction {
+    UP,
+    RIGHT,
+    DOWN,
+    LEFT
+}; 
+
+struct State {
+    int x;
+    int y;
+    Direction direction;
+
+    bool operator==(const State& other) const {
+        return x == other.x && y == other.y && direction == other.direction;
     }
-    
+};
+
+namespace std {
+    template <>
+    struct hash<State> {
+        std::size_t operator()(const State& s) const {
+            return std::hash<int>{}(s.x) ^ std::hash<int>{}(s.y) ^ std::hash<int>{}(s.direction);
+        }
+    };
+}
+
+bool position_in_bounds(const std::vector<std::string>& path_map, int x, int y) {
+    return x >= 0 && y >= 0 && x < path_map.size() && y < path_map[0].size();
+}
+
+int part_1() {
+    std::istringstream input_stream(content);
+    std::string line;
+    std::vector<std::string> path_map;
+
+    int row{0};
+    State state;
+    while (std::getline(input_stream, line)) {
+        if(line.empty()) {
+            continue;
+        }        
+        path_map.emplace_back(line); 
+        if(line.find('^') != std::string::npos) {
+            state.x = row;
+            state.y = line.find('^');
+            state.direction = UP;
+        }
+        row++;
+    }
+
+    auto unique_acc{0};
+    while (position_in_bounds(path_map, state.x, state.y)) {
+        int walk_x{state.x};
+        int walk_y{state.y};
+
+        switch(state.direction) {
+            case UP:
+                walk_x--;
+                break;
+            case RIGHT:
+                walk_y++;
+                break;
+            case DOWN:
+                walk_x++;
+                break;
+            case LEFT:
+                walk_y--;
+                break;
+            default:
+                break;
+         }
+
+        if(!position_in_bounds(path_map, walk_x, walk_y)) {
+            break;
+        } else if(path_map[walk_x][walk_y] == '#') {
+            state.direction = static_cast<Direction>((state.direction + 1) % 4);
+        } else {
+            state.x = walk_x;
+            state.y = walk_y;
+
+            if(path_map[state.x][state.y] != 'X') {
+                unique_acc++;
+                path_map[state.x][state.y] = 'X';
+            } 
+        }
+    }
+    return unique_acc;
+}
+
+bool loop_detected(std::vector<std::string>& path_map, State start_state) {
+    std::unordered_set<State> visited_states;
+
+    State state = start_state;
+    while(position_in_bounds(path_map, state.x, state.y)) {
+        int walk_x{state.x};
+        int walk_y{state.y};
+
+        switch(state.direction) {
+            case UP:
+                walk_x--;
+                break;
+            case RIGHT:
+                walk_y++;
+                break;
+            case DOWN:
+                walk_x++;
+                break;
+            case LEFT:
+                walk_y--;
+                break;
+            default:
+                break;
+         }
+
+        if(!position_in_bounds(path_map, walk_x, walk_y)) {
+            return false;
+        } else if(path_map[walk_x][walk_y] == '#') {
+            state.direction = static_cast<Direction>((state.direction + 1) % 4);
+        } else {
+            state.x = walk_x;
+            state.y = walk_y;
+            if(visited_states.find(state) != visited_states.end()) {
+                return true;
+            } else {
+                visited_states.insert(state);
+            }
+        }
+    }
+
+    return false;
+}
+
+
+int part_2() {
+    std::istringstream input_stream(content);
+    std::string line;
+    std::vector<std::string> path_map;
+    std::unordered_set<State> obstacles;
+
+    int row{0};
+    State state;
+    while (std::getline(input_stream, line)) {
+        if(line.empty()) continue;
+
+        path_map.emplace_back(line); 
+        if(line.find('^') != std::string::npos) {
+            state.x = row;
+            state.y = line.find('^');
+            state.direction = UP;
+        }
+        row++;
+    }
+    State start_state = state;
+    while (position_in_bounds(path_map, state.x, state.y)) {
+        int walk_x{state.x};
+        int walk_y{state.y};
+
+        switch(state.direction) {
+            case UP:
+                walk_x--;
+                break;
+            case RIGHT:
+                walk_y++;
+                break;
+            case DOWN:
+                walk_x++;
+                break;
+            case LEFT:
+                walk_y--;
+                break;
+            default:
+                break;
+         }
+
+        if(!position_in_bounds(path_map, walk_x, walk_y)) {
+            break;
+        } else if(path_map[walk_x][walk_y] == '#') {
+            state.direction = static_cast<Direction>((state.direction + 1) % 4);
+        } else {
+            if(!(start_state.x == walk_x && walk_y == start_state.y)) {
+                path_map[walk_x][walk_y] = '#';
+                if(loop_detected(path_map, start_state) && obstacles.find({walk_x, walk_y}) == obstacles.end()) {
+                    obstacles.insert({walk_x, walk_y});
+                } 
+                path_map[walk_x][walk_y] = '.';
+            }
+            state.x = walk_x;
+            state.y = walk_y;
+        }
+
+    }
+
+    return obstacles.size();
+}
+
+int main() {
+    std::chrono::steady_clock::time_point begin = std::chrono::steady_clock::now();
+    auto p1_val = part_1();
+    std::chrono::steady_clock::time_point middle = std::chrono::steady_clock::now();
+    auto p2_val = part_2();
+    std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
+    cout << "Part 1: " << p1_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(middle - begin).count() << "µs)" << endl;  
+    cout << "Part 2: " << p2_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(end - middle).count() << "µs)" << endl;
     return 0;
 }