diff --git a/day21/deno.json b/day21/deno.json
new file mode 100644
index 0000000..c6e0315
--- /dev/null
+++ b/day21/deno.json
@@ -0,0 +1,7 @@
+{
+  "name": "@scope/day21",
+  "version": "0.1.0",
+  "exports": {
+    ".": "./mod.ts"
+  }
+}
diff --git a/day21/example.txt b/day21/example.txt
new file mode 100644
index 0000000..4cf0c29
--- /dev/null
+++ b/day21/example.txt
@@ -0,0 +1,5 @@
+029A
+980A
+179A
+456A
+379A
diff --git a/day21/mod.ts b/day21/mod.ts
new file mode 100644
index 0000000..7e8e84c
--- /dev/null
+++ b/day21/mod.ts
@@ -0,0 +1,225 @@
+import { BinaryHeap } from "jsr:@std/data-structures";
+
+type Keypad = string[][];
+
+const PIN_PAD: Keypad = [
+  ["7", "8", "9"],
+  ["4", "5", "6"],
+  ["1", "2", "3"],
+  ["", "0", "A"],
+];
+
+const DIRECTIONAL_PAD: Keypad = [
+  ["", "^", "A"],
+  ["<", "v", ">"],
+];
+
+function bfs(keypad: Keypad, paths: Map<string, [number, Set<string>]>) {
+  for (let i = 0; i < keypad.length; i++) {
+    for (let j = 0; j < keypad[i].length; j++) {
+      if (keypad[i][j] === "") {
+        continue;
+      }
+      const key = `${keypad[i][j]},${keypad[i][j]}`;
+      paths.set(key, [0, new Set([""])]);
+    }
+  }
+
+  const directions = [
+    [0, 1, ">"],
+    [0, -1, "<"],
+    [1, 0, "v"],
+    [-1, 0, "^"],
+  ] as [number, number, string][];
+
+  const heap = new BinaryHeap<[string, string, string]>(
+    ([, , a], [, , b]) => a.length - b.length,
+  );
+
+  const neighbors = new Map<string, string>();
+
+  for (let i = 0; i < keypad.length; i++) {
+    for (let j = 0; j < keypad[i].length; j++) {
+      if (keypad[i][j] === "") {
+        continue;
+      }
+      for (const [di, dj, dir] of directions) {
+        const ni = i + di;
+        const nj = j + dj;
+        if (
+          ni >= 0 &&
+          ni < keypad.length &&
+          nj >= 0 &&
+          nj < keypad[ni].length &&
+          keypad[ni][nj] !== ""
+        ) {
+          const key = `${keypad[i][j]},${keypad[ni][nj]}`;
+          neighbors.set(key, dir);
+          heap.push([keypad[i][j], keypad[ni][nj], dir]);
+        }
+      }
+    }
+  }
+
+  while (!heap.isEmpty()) {
+    const [from, to, dir] = heap.pop()!;
+    const key = `${from},${to}`;
+
+    if (paths.has(key)) {
+      const [storedSize, storedPaths] = paths.get(key)!;
+      if (dir.length > storedSize) {
+        continue;
+      }
+
+      if (dir.length == storedSize) {
+        if (storedPaths.has(dir)) {
+          continue;
+        }
+
+        storedPaths.add(dir);
+      }
+
+      if (dir.length < storedSize) {
+        storedPaths.clear();
+        storedPaths.add(dir);
+        paths.set(key, [dir.length, storedPaths]);
+      }
+    } else {
+      paths.set(key, [dir.length, new Set([dir])]);
+    }
+
+    for (const [nkey, ndir] of neighbors) {
+      const [nfrom, nto] = nkey.split(",") as [string, string];
+      if (nto === from) {
+        heap.push([nfrom, to, ndir + dir]);
+      }
+
+      if (to === nfrom) {
+        heap.push([from, nto, dir + ndir]);
+      }
+    }
+
+    for (const [nkey, [nsize, ndirs]] of paths) {
+      if (nsize == 0) continue;
+      const [nfrom, nto] = nkey.split(",") as [string, string];
+      if (nto === from) {
+        for (const ndir of ndirs.values()) {
+          heap.push([nfrom, to, ndir + dir]);
+        }
+      }
+
+      if (to === nfrom) {
+        for (const ndir of ndirs.values()) {
+          heap.push([from, nto, dir + ndir]);
+        }
+      }
+    }
+  }
+}
+
+function calculateShortestSequence(
+  code: string,
+  numRobots: number,
+  pinPadPaths: Map<string, [number, Set<string>]>,
+  directionalPadPaths: Map<string, [number, Set<string>]>,
+): number {
+  const memo: Map<string, number> = new Map();
+
+  function solve(
+    robotIndex: number,
+    currentKey: string,
+    remainingCode: string,
+  ): number {
+    const memoKey = `${robotIndex},${currentKey},${remainingCode}`;
+    if (memo.has(memoKey)) {
+      return memo.get(memoKey)!;
+    }
+
+    if (remainingCode.length === 0) {
+      return 0;
+    }
+
+    if (robotIndex === 0) {
+      return remainingCode.length;
+    }
+
+    let totalCost = 0;
+
+    let loopCurrentKey = currentKey;
+
+    for (const nextKey of remainingCode) {
+      let minCost = Infinity;
+
+      const pathsKey = `${loopCurrentKey},${nextKey}`;
+
+      let paths;
+
+      if (robotIndex === numRobots) {
+        [, paths] = pinPadPaths.get(pathsKey)!;
+      } else {
+        [, paths] = directionalPadPaths.get(pathsKey)!;
+      }
+
+      for (const path of paths) {
+        const cost = solve(
+          robotIndex - 1,
+          "A",
+          path + "A",
+        );
+        minCost = Math.min(minCost, cost);
+      }
+
+      totalCost += minCost;
+      loopCurrentKey = nextKey;
+    }
+
+    memo.set(memoKey, totalCost);
+    return totalCost;
+  }
+
+  return solve(numRobots, "A", code);
+}
+
+export function parse(data: string): string[] {
+  return data.trim().split("\n").map((line) => line.trim());
+}
+
+export function solve(data: string[], numRobots: number): number {
+  const pinPadPaths = new Map<string, [number, Set<string>]>();
+  const dirPadPaths = new Map<string, [number, Set<string>]>();
+
+  bfs(PIN_PAD, pinPadPaths);
+  bfs(DIRECTIONAL_PAD, dirPadPaths);
+
+  return data.map((line) => {
+    const shortestLength = calculateShortestSequence(
+      line,
+      numRobots,
+      pinPadPaths,
+      dirPadPaths,
+    );
+
+    const num = Number(
+      line.split("").map((c) => Number(c)).filter((n) => !Number.isNaN(n)).join(
+        "",
+      ),
+    );
+
+    return shortestLength * num;
+  }).reduce((acc, val) => acc + val, 0);
+}
+
+export function solve1(data: string[]): number {
+  return solve(data, 3);
+}
+
+export function solve2(data: string[]): number {
+  return solve(data, 26);
+}
+
+if (import.meta.main) {
+  const dataPath = new URL("input.txt", import.meta.url).pathname;
+  const data = parse(await Deno.readTextFile(dataPath));
+  console.log(solve1(data));
+  console.log(solve2(data));
+}
diff --git a/day21/test.ts b/day21/test.ts
new file mode 100644
index 0000000..23c74ea
--- /dev/null
+++ b/day21/test.ts
@@ -0,0 +1,9 @@
+import { assertEquals } from "@std/assert";
+import { parse, solve1, solve2 } from "./mod.ts";
+
+Deno.test(async function testExample() {
+  const dataPath = new URL("example.txt", import.meta.url).pathname;
+  const data = parse(await Deno.readTextFile(dataPath));
+  assertEquals(solve1(data), 126384);
+  assertEquals(solve2(data), 154115708116294);
+});