2024 day 6 cleanup

pvainio · pvainio · commit 536ea2a56322 · 2024-12-06T19:50:30.000+02:00
diff --git a/2024/js/day6.js b/2024/js/day6.js
@@ -6,7 +6,8 @@ const dirs = { '^': [0, -1, '>'], 'v': [0, 1, '<'], '<': [-1, 0, '^'], '>': [1,
 const findPosAndDir = (map) => map.flatMap((r, y) => r.flatMap((c, x) => dirs[c] ? [x, y, c] : null).filter(p => p !== null));
 const outOfBounds = (map, x, y) => x < 0 || x > map[0].length - 1 || y < 0 || y > map.length - 1;
 
-const patrol = (map, x, y, dir) => {
+const patrol = (map, obs) => {
+  let [x, y, dir] = findPosAndDir(map);
   const route = [];
   while (true) {
     const posAndDir = `${x},${y} ${dir}`;
@@ -15,24 +16,22 @@ const patrol = (map, x, y, dir) => {
     const [dx, dy, rotate] = dirs[dir];
     const [nx, ny] = [x + dx, y + dy];
     if (outOfBounds(map, nx, ny)) return route;
-    if (map[ny][nx] == '#') dir = rotate;
+    if (map[ny][nx] == '#' || (obs?.x == nx && obs?.y == ny)) dir = rotate;
     else [x, y] = [nx, ny];
   }
 }
 
-const [startx, starty, startdir] = findPosAndDir(map);
-const route = patrol(map, startx, starty, startdir);
+const route = patrol(map);
 const positions = route.map(posAndDir => posAndDir.split(' ')[0]);
 const uniqPositions = [...new Set(positions)];
 console.log(`day6a: ${uniqPositions.length}`);
 
+const firstPosition = positions[0];
 // try adding obstacle to visited position on route and check for loop
 const loop = uniqPositions.filter(pos => {
+  if (pos == firstPosition) return false; // not allowed to add obstacle to start
   const [x, y] = pos.split(',').map(Number);
-  if (x == startx && y == starty) return false; // not allowed to add obstacle to start
-  const nmap = JSON.parse(JSON.stringify(map)); // deep clone
-  nmap[y][x] = '#'; // add new obstacle
-  return patrol(nmap, startx, starty, startdir) == null; //
+  return patrol(map, {x, y}) == null; // patrol returns null in case of loop
 });
 const uniqLoop = new Set(loop);
 console.log(`day6b: ${uniqLoop.size}`);
