🚀 faster solution

packages/compute/pruneLayer.ts

@@ -0,0 +1,85 @@
+import { getColor, isEmpty, isInside, setColorEmpty } from "./grid";
+import { around4 } from "./point";
+import { sortPush } from "./utils/sortPush";
+import type { Color, Grid } from "./grid";
+import type { Point } from "./point";
+
+type M = Point & { parent: M | null; h: number };
+
+const unwrap = (grid: Grid, m: M | null): Point[] =>
+  m ? [...unwrap(grid, m.parent), m] : [];
+
+const getEscapePath = (
+  grid: Grid,
+  x: number,
+  y: number,
+  color: Color,
+  forbidden: Point[] = []
+) => {
+  const openList: M[] = [{ x, y, h: 0, parent: null }];
+  const closeList: Point[] = [];
+
+  while (openList.length) {
+    const c = openList.shift()!;
+
+    if (c.y === -1 || c.y === grid.height) return unwrap(grid, c);
+
+    for (const a of around4) {
+      const x = c.x + a.x;
+      const y = c.y + a.y;
+
+      if (!forbidden.some((cl) => cl.x === x && cl.y === y)) {
+        if (!isInside(grid, x, y))
+          return unwrap(grid, { x, y, parent: c } as any);
+
+        const u = getColor(grid, x, y);
+
+        if (
+          (isEmpty(u) || u <= color) &&
+          !closeList.some((cl) => cl.x === x && cl.y === y)
+        ) {
+          const h = Math.abs(grid.height / 2 - y);
+          const o = { x, y, parent: c, h };
+
+          sortPush(openList, o, (a, b) => a.h - b.h);
+          closeList.push(o);
+          openList.push(o);
+        }
+      }
+    }
+  }
+
+  return null;
+};
+
+const isFree = (
+  grid: Grid,
+  x: number,
+  y: number,
+  color: Color,
+  snakeN: number
+) => {
+  const one = getEscapePath(grid, x, y, color);
+
+  if (!one) return false;
+
+  const two = getEscapePath(grid, x, y, color, one.slice(0, snakeN));
+
+  return !!two;
+};
+
+export const pruneLayer = (grid: Grid, color: Color, snakeN: number) => {
+  const chunk: Point[] = [];
+
+  for (let x = grid.width; x--; )
+    for (let y = grid.height; y--; ) {
+      const c = getColor(grid, x, y);
+
+      if (!isEmpty(c) && c <= color && isFree(grid, x, y, color, snakeN)) {
+        setColorEmpty(grid, x, y);
+        chunk.push({ x, y });
+      }
+    }
+
+  return chunk;
+};