c 2024 6 part 1

c/2024/6/guard_gallivant.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+typedef enum Direction { RIGHT, UP, LEFT, DOWN } Direction;
+
+typedef struct Position {
+  int x;
+  int y;
+} Position;
+
+typedef struct Game {
+  char *map;
+  int width;
+  int height;
+  Position guard;
+  Direction guard_direction;
+  int position_count;
+} Game;
+
+Position position_from_index(Game *game, int index) {
+  Position p = { index % game->width, index / game->width };
+  return p;
+}
+
+int index_from_position(Game *game, Position p) {
+  return p.x + (game->width * p.y);
+}
+
+bool position_inbounds(Game *game, Position p) {
+  return p.x >= 0 && p.y >= 0 && p.x < game->width && p.y < game->height;
+}
+
+bool guard_inbounds(Game *game) {
+  return position_inbounds(game, game -> guard);
+}
+
+bool position_has_obstacle(Game *game, Position p) {
+  return game->map[index_from_position(game, p)] == '#';
+}
+
+void turn_guard(Game *game) {
+  Direction new_direction;
+  switch (game->guard_direction) {
+  case RIGHT:
+    new_direction = DOWN;
+    break;
+  case UP:
+    new_direction = RIGHT;
+    break;
+  case LEFT:
+    new_direction = UP;
+    break;
+  case DOWN:
+    new_direction = LEFT;
+    break;
+  }
+  game->guard_direction = new_direction;
+}
+
+void move_guard(Game *game) {
+  Position target;
+  target.x = game->guard.x;
+  target.y = game->guard.y;
+  switch (game->guard_direction) {
+  case RIGHT:
+    target.x++;
+    break;
+  case UP:
+    target.y--;
+    break;
+  case LEFT:
+    target.x--;
+    break;
+  case DOWN:
+    target.y++;
+    break;
+  }
+
+  if (position_has_obstacle(game, target)) turn_guard(game);
+  else {
+    if (game->map[index_from_position(game, game->guard)] == '.') {
+      game->map[index_from_position(game, game->guard)] = 'X';
+      game->position_count++;
+    }
+      
+    game->guard.x = target.x;
+    game->guard.y = target.y;
+  }
+}
+
+int main() {
+  char *line;
+  Game game;
+  game.map = aoc_read_input();
+  game.width = strchr(game.map, '\n') - game.map + 1;
+  game.height = strlen(game.map) / game.width;
+  game.position_count = 0;
+  for (int i = 0; i < strlen(game.map); i++) {
+    if (game.map[i] == '^') {
+      game.map[i] = '.';
+      game.guard = position_from_index(&game, i);
+      game.guard_direction = UP;
+      break;
+    }
+  }
+
+  while (guard_inbounds(&game)) {
+    move_guard(&game);
+  }
+
+  printf("Part 1: %d\n", game.position_count);
+
+  aoc_free();
+  return 0;
+}