Add solutions to day 10

Author: maxdavidson

src/day10/day10.test.ts

@@ -0,0 +1,21 @@
+import * as fs from "node:fs/promises";
+import { suite, test } from "node:test";
+
+import { part1, part2 } from "./day10.ts";
+
+const [INPUT, INPUT_TEST] = await Promise.all([
+  fs.readFile(new URL("input.txt", import.meta.url), "utf-8"),
+  fs.readFile(new URL("input-test.txt", import.meta.url), "utf-8"),
+]);
+
+suite("day10", () => {
+  test("part1", (t) => {
+    t.assert.equal(part1(INPUT_TEST), 36);
+    t.assert.equal(part1(INPUT), 629);
+  });
+
+  test("part2", (t) => {
+    t.assert.equal(part2(INPUT_TEST), 81);
+    t.assert.equal(part2(INPUT), 1242);
+  });
+});

src/day10/day10.ts

@@ -0,0 +1,63 @@
+import { lines } from "../utils.ts";
+
+function trails(input: string): IteratorObject<IteratorObject<number>> {
+  const map = lines(input).flatMap(Iterator.from).map(Number).toArray();
+
+  const size = Math.sqrt(map.length);
+
+  if (!Number.isInteger(size)) {
+    throw new TypeError("Not a square!");
+  }
+
+  function* endPositions(
+    pos: number,
+    expectedValue: number,
+  ): Generator<number> {
+    const value = map[pos]!;
+
+    if (value !== expectedValue) {
+      return;
+    }
+
+    if (value === 9) {
+      yield pos;
+      return;
+    }
+
+    const x = pos % size;
+    const y = (pos - x) / size;
+
+    if (0 <= x - 1) {
+      yield* endPositions(size * y + (x - 1), value + 1);
+    }
+
+    if (0 <= y - 1) {
+      yield* endPositions(size * (y - 1) + x, value + 1);
+    }
+
+    if (x + 1 < size) {
+      yield* endPositions(size * y + (x + 1), value + 1);
+    }
+
+    if (y + 1 < size) {
+      yield* endPositions(size * (y + 1) + x, value + 1);
+    }
+  }
+
+  return map
+    .entries()
+    .filter(([_pos, value]) => value === 0)
+    .map(([pos, _value]) => endPositions(pos, 0));
+}
+
+export function part1(input: string): number {
+  return trails(input)
+    .map((trail) => new Set(trail).size)
+    .reduce((a, b) => a + b, 0);
+}
+
+export function part2(input: string): number {
+  return trails(input)
+    .map((trail) => trail.toArray().length)
+    .reduce((a, b) => a + b, 0);
+}

src/day10/input-test.txt

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

src/day10/input.txt

@@ -0,0 +1,50 @@
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