feat: 2024 Day 21

Author: mfulton26

2024/day/21/part/1/solve.test.ts

@@ -0,0 +1,14 @@
+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+029A
+980A
+179A
+456A
+379A`;
+
+  assertEquals(solve(input), 126384);
+});

2024/day/21/part/1/solve.ts

@@ -0,0 +1,49 @@
+type Paths = Record<string, Record<string, string>>;
+
+const numericKeypadPaths: Paths = Object.fromEntries(
+  [
+    ["", "^<", "^", "^>", "^^<", "^^", "^^>", "^^^<", "^^^", "^^^>", ">"],
+    [">v", "", ">", ">>", "^", "^>", "^>>", "^^", "^^>", "^^>>", ">>v"],
+    ["v", "<", "", ">", "<^", "^", "^>", "<^^", "^^", "^^>", "v>"],
+    ["<v", "<<", "<", "", "<<^", "<^", "^", "<<^^", "<^^", "^^", "v"],
+    [">vv", "v", "v>", "v>>", "", ">", ">>", "^", "^>", "^>>", ">>vv"],
+    ["vv", "<v", "v", "v>", "<", "", ">", "<^", "^", "^>", "vv>"],
+    ["<vv", "<<v", "<v", "v", "<<", "<", "", "<<^", "<^", "^", "vv"],
+    [">vvv", "vv", "vv>", "vv>>", "v", "v>", "v>>", "", ">", ">>", ">>vvv"],
+    ["vvv", "<vv", "vv", "vv>", "<v", "v", "v>", "<", "", ">", "vvv>"],
+    ["<vvv", "<<vv", "<vv", "vv", "<<v", "<v", "v", "<<", "<", "", "vvv"],
+    ["<", "^<<", "<^", "^", "^^<<", "<^^", "^^", "^^^<<", "<^^^", "^^^", ""],
+  ].map((row, u) => [
+    u.toString(11).toUpperCase(),
+    Object.fromEntries(row.map((p, v) => [v.toString(11).toUpperCase(), p])),
+  ]),
+);
+
+const directionalKeypadPaths: Paths = {
+  "^": { "^": "", "v": "v", "<": "v<", ">": "v>", "A": ">" },
+  "v": { "^": "^", "v": "", "<": "<", ">": ">", "A": "^>" },
+  "<": { "^": ">^", "v": ">", "<": "", ">": ">>", "A": ">>^" },
+  ">": { "^": "<^", "v": "<", "<": "<<", ">": "", "A": "^" },
+  "A": { "^": "<", "v": "<v", "<": "v<<", ">": "v", "A": "" },
+};
+
+export default function solve(input: string) {
+  const codes = input.split("\n");
+  let sum = 0;
+  for (const code of codes) {
+    let path = code;
+    for (let i = 0; i <= 2; i++) {
+      let nextPath = "";
+      let pointer = "A";
+      const paths = i === 0 ? numericKeypadPaths : directionalKeypadPaths;
+      for (const char of path) {
+        nextPath += paths[pointer][char];
+        nextPath += "A";
+        pointer = char;
+      }
+      path = nextPath;
+    }
+    sum += path.length * parseInt(code);
+  }
+  return sum;
+}

2024/day/21/part/2/solve.test.ts

@@ -0,0 +1,14 @@
+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+029A
+980A
+179A
+456A
+379A`;
+
+  assertEquals(solve(input, { depth: 2 }), 126384);
+});

2024/day/21/part/2/solve.ts

@@ -0,0 +1,63 @@
+type Paths = Record<string, Record<string, string>>;
+
+const numericKeypadPaths: Paths = Object.fromEntries(
+  [
+    ["", "^<", "^", "^>", "^^<", "^^", "^^>", "^^^<", "^^^", "^^^>", ">"],
+    [">v", "", ">", ">>", "^", "^>", "^>>", "^^", "^^>", "^^>>", ">>v"],
+    ["v", "<", "", ">", "<^", "^", "^>", "<^^", "^^", "^^>", "v>"],
+    ["<v", "<<", "<", "", "<<^", "<^", "^", "<<^^", "<^^", "^^", "v"],
+    [">vv", "v", "v>", "v>>", "", ">", ">>", "^", "^>", "^>>", ">>vv"],
+    ["vv", "<v", "v", "v>", "<", "", ">", "<^", "^", "^>", "vv>"],
+    ["<vv", "<<v", "<v", "v", "<<", "<", "", "<<^", "<^", "^", "vv"],
+    [">vvv", "vv", "vv>", "vv>>", "v", "v>", "v>>", "", ">", ">>", ">>vvv"],
+    ["vvv", "<vv", "vv", "vv>", "<v", "v", "v>", "<", "", ">", "vvv>"],
+    ["<vvv", "<<vv", "<vv", "vv", "<<v", "<v", "v", "<<", "<", "", "vvv"],
+    ["<", "^<<", "<^", "^", "^^<<", "<^^", "^^", "^^^<<", "<^^^", "^^^", ""],
+  ].map((row, u) => [
+    u.toString(11).toUpperCase(),
+    Object.fromEntries(row.map((p, v) => [v.toString(11).toUpperCase(), p])),
+  ]),
+);
+
+const directionalKeypadPaths: Paths = {
+  "^": { "^": "", "v": "v", "<": "v<", ">": "v>", "A": ">" },
+  "v": { "^": "^", "v": "", "<": "<", ">": ">", "A": "^>" },
+  "<": { "^": ">^", "v": ">", "<": "", ">": ">>", "A": ">>^" },
+  ">": { "^": "<^", "v": "<", "<": "<<", ">": "", "A": "^" },
+  "A": { "^": "<", "v": "<v", "<": "v<<", ">": "v", "A": "" },
+};
+
+function findShortestSequenceLength(
+  code: string,
+  depth: number,
+  {
+    paths = numericKeypadPaths,
+    seen = new Map<`${number},${string}`, number>(),
+  } = {},
+): number {
+  if (depth < 0) return code.length;
+  const hash = `${depth},${code}` as const;
+  if (seen.has(hash)) return seen.get(hash)!;
+  let result = 0;
+  let pointer = "A";
+  const options = { paths: directionalKeypadPaths, seen };
+  for (const char of code) {
+    result += findShortestSequenceLength(
+      `${paths[pointer][char]}A`,
+      depth - 1,
+      options,
+    );
+    pointer = char;
+  }
+  seen.set(hash, result);
+  return result;
+}
+
+export default function solve(input: string, { depth = 25 } = {}) {
+  const codes = input.split("\n");
+  let sum = 0;
+  for (const code of codes) {
+    sum += findShortestSequenceLength(code, depth) * parseInt(code);
+  }
+  return sum;
+}