+day06 part1

2024/day06/input

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2024/day06/part1.cc

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+#include <iostream>
+#include <vector>
+#include <string>
+
+class vec {
+public:
+  int x;
+  int y;
+  vec(int x, int y) : x(x), y(y) {}
+  vec operator+(const vec& other) const;
+  int index(int width) const;
+  vec right() const;
+};
+
+vec vec::operator+(const vec& other) const {
+  return vec{x + other.x, y + other.y};
+}
+
+int vec::index(int width) const {
+  return y * width + x;
+}
+
+vec vec::right() const {
+  return vec{-y, x};
+}
+
+class grid {
+  int width;
+  int height;
+  std::vector<bool> obstacles;
+  std::vector<bool> visited;
+  int visit_count = 0;
+public:
+  grid(int width, int height);
+  bool visit(const vec& v);
+  void obstacle(const vec& v);
+  bool is_obstacle(const vec& v) const;
+  bool is_valid(const vec& v) const;
+  int count() const;
+};
+
+grid::grid(int width, int height)
+    : width(width), height(height) {
+  obstacles.resize(width * height);
+  visited.resize(width * height);
+}
+
+bool grid::visit(const vec& v) {
+  if (visited[v.index(width)]) {
+    return true;
+  }
+  visited[v.index(width)] = true;
+  visit_count++;
+  return false;
+}
+
+void grid::obstacle(const vec& v) {
+  obstacles[v.index(width)] = true;
+}
+
+bool grid::is_obstacle(const vec& v) const {
+  return obstacles.at(v.index(width));
+}
+
+bool grid::is_valid(const vec& v) const {
+  return v.x >= 0 && v.x < width
+    && v.y >= 0 && v.y < height;
+}
+
+int grid::count() const {
+  return visit_count;
+}
+
+int main() {
+  int width = 0, height = 0;
+  std::string line;
+  std::vector<vec> obstacles;
+  vec pos{0, 0};
+  vec dir{0, -1};
+  for (int line_num = 0; getline(std::cin, line); line_num++) {
+    height++;
+    for (int x = 0; x < line.size(); x++) {
+      if (line[x] == '#') {
+        obstacles.emplace_back(x, line_num);
+      } else if (line[x] == '^') {
+        pos = vec{x, line_num};
+      }
+    }
+  }
+  width = line.size();
+  grid g{width, height};
+  for (const vec& v : obstacles) {
+    g.obstacle(v);
+  }
+  for (;; pos = pos + dir) {
+    g.visit(pos);
+    if (!g.is_valid(pos + dir)) {
+      break;
+    }
+    while (g.is_obstacle(pos + dir)) {
+      dir = dir.right();
+    }
+  }
+  std::cout << g.count() << std::endl;
+  return EXIT_SUCCESS;
+}