solve day 1

Author: shahata

src/2025/day01.js

@@ -0,0 +1,48 @@
+export function part1(input) {
+  let password = 0;
+  input
+    .split("\n")
+    .map(x => {
+      let [, direction, count] = x.match(/(L|R)(\d+)/);
+      return { direction, count: +count };
+    })
+    .reduce((prev, curr) => {
+      if (curr.direction === "L") prev -= curr.count;
+      if (curr.direction === "R") prev += curr.count;
+      while (prev < 0) prev += 100;
+      while (prev >= 100) prev -= 100;
+      if (prev === 0) password++;
+      return prev;
+    }, 50);
+
+  return password;
+}
+
+export function part2(input) {
+  let password = 0;
+  input
+    .split("\n")
+    .map(x => {
+      let [, direction, count] = x.match(/(L|R)(\d+)/);
+      return { direction, count: +count };
+    })
+    .reduce((prev, curr) => {
+      if (curr.direction === "L") {
+        for (let i = 0; i < curr.count; i++) {
+          prev--;
+          if (prev === 0) password++;
+          if (prev === -1) prev = 99;
+        }
+      }
+      if (curr.direction === "R") {
+        for (let i = 0; i < curr.count; i++) {
+          prev++;
+          if (prev === 100) prev = 0;
+          if (prev === 0) password++;
+        }
+      }
+      return prev;
+    }, 50);
+
+  return password;
+}

src/2025/day01.test.js

@@ -0,0 +1,57 @@
+import { part1, part2 } from "./day01.js";
+import { describe, test, expect } from "vitest";
+import readInput from "../utils/read-input.js";
+
+let input = readInput(import.meta.url);
+
+describe("day01 2025", () => {
+  describe("part1", () => {
+    test("it should work for part 1 examples", () => {
+      expect(
+        part1(
+          [
+            "L68",
+            "L30",
+            "R48",
+            "L5",
+            "R60",
+            "L55",
+            "L1",
+            "L99",
+            "R14",
+            "L82",
+          ].join("\n"),
+        ),
+      ).toEqual(3);
+    });
+
+    test("it should work for part 1 input", () => {
+      expect(part1(input)).toEqual(1150);
+    });
+  });
+
+  describe("part2", () => {
+    test("it should work for part 2 examples", () => {
+      expect(
+        part2(
+          [
+            "L68",
+            "L30",
+            "R48",
+            "L5",
+            "R60",
+            "L55",
+            "L1",
+            "L99",
+            "R14",
+            "L82",
+          ].join("\n"),
+        ),
+      ).toEqual(6);
+    });
+
+    test("it should work for part 2 input", () => {
+      expect(part2(input)).toEqual(6738);
+    });
+  });
+});