down to 20 secs

src/2023/day23.js

@@ -1,43 +1,43 @@
-function addTeleports(map) {
+function findTeleports(map) {
   const teleports = {};
   for (let y = 0; y < map.length; y++) {
-    for (let x = 0; x < map.length; x++) {
+    for (let x = 0; x < map[0].length; x++) {
       if (map[y][x] === '#') continue;
-      const neighbors = getNeighbors(map, { x, y }, []);
+      const neighbors = getNeighbors(map, { x, y });
       if (neighbors.length === 2) continue;
       neighbors.forEach(n => {
+        let neighbors;
+        let curr = n;
         let prev = { x, y };
-        const trail = [prev];
-        while (n) {
-          const neighbors = getNeighbors(map, n, [`${prev.x},${prev.y}`]);
-          trail.push(n);
-          prev = n;
-          if (neighbors.length === 1) n = neighbors[0];
-          else n = null;
-        }
-        if (trail.length > 2) {
-          const key1 = `${trail.at(1).x},${trail.at(1).y}`;
-          const key2 = `${trail.at(-2).x},${trail.at(-2).y}`;
-          teleports[key1] = { dest: trail.at(-1), steps: trail.length - 2 };
-          teleports[key2] = { dest: trail.at(0), steps: trail.length - 2 };
-        }
+        let steps = -1;
+        do {
+          neighbors = getNeighbors(map, curr, [`${prev.x},${prev.y}`]);
+          steps++;
+          prev = curr;
+          curr = neighbors[0];
+        } while (neighbors.length === 1);
+        if (steps > 0) teleports[`${n.x},${n.y}`] = { dest: prev, steps };
       });
     }
   }
   return teleports;
 }
 
-function getNeighbors(map, { x, y }, visited) {
+function getNeighbors(map, { x, y, steps = 0 }, visited = [], teleports = {}) {
   let neighbors = [
-    { x: x + 1, y },
-    { x: x - 1, y },
-    { x, y: y + 1 },
-    { x, y: y - 1 },
+    { x: x + 1, y, steps: steps + 1 },
+    { x: x - 1, y, steps: steps + 1 },
+    { x, y: y + 1, steps: steps + 1 },
+    { x, y: y - 1, steps: steps + 1 },
   ];
   if (map[y][x] === '>') neighbors = [neighbors[0]];
   if (map[y][x] === '<') neighbors = [neighbors[1]];
   if (map[y][x] === 'v') neighbors = [neighbors[2]];
   if (map[y][x] === '^') neighbors = [neighbors[3]];
+  neighbors = neighbors.map(n => {
+    const { dest, steps } = teleports[`${n.x},${n.y}`] || {};
+    return dest ? { ...dest, steps: n.steps + steps } : n;
+  });
   return neighbors.filter(
     n =>
       map[n.y]?.[n.x] &&
@@ -52,27 +52,17 @@ function solve(map, teleports, start, end) {
   const stack = [start];
   while (stack.length > 0) {
     const next = stack.pop();
-    while (path.length > next.len) path.pop();
-    path.push(`${next.x},${next.y}`);
-    if (next.x === end.x && next.y === end.y) {
-      best = Math.max(best, next.steps);
-    } else if (teleports[`${next.x},${next.y}`]) {
-      const { dest, steps } = teleports[`${next.x},${next.y}`];
-      if (!path.includes(`${dest.x},${dest.y}`)) {
-        stack.push({ ...dest, steps: next.steps + steps, len: path.length });
-      }
-    } else {
-      getNeighbors(map, next, path).forEach(n =>
-        stack.push({ ...n, steps: next.steps + 1, len: path.length }),
-      );
-    }
+    path.splice(next.len, Infinity, `${next.x},${next.y}`);
+    if (next.x === end.x && next.y === end.y) best = Math.max(best, next.steps);
+    const neighbors = getNeighbors(map, next, path, teleports);
+    neighbors.forEach(n => stack.push({ ...n, len: path.length }));
   }
   return best;
 }
 
 export function part1(input) {
   const map = input.split('\n').map(line => line.split(''));
-  const teleports = addTeleports(map);
+  const teleports = findTeleports(map);
   let start = { x: 1, y: 0, steps: 0, len: 0 };
   let end = { x: map.length - 2, y: map.length - 1 };
   return solve(map, teleports, start, end);