From c728436ed7c4ff06cb2a10f500771b0d0dbbd2ce Mon Sep 17 00:00:00 2001
From: Naomi Carrigan <commits@nhcarrigan.com>
Date: Tue, 2 Dec 2025 12:06:20 -0800
Subject: [PATCH] feat: advent of code day two

---
 src/advent-of-code/2025/day2/inputOne.txt |  1 +
 src/advent-of-code/2025/day2/main.spec.ts | 34 ++++++++++
 src/advent-of-code/2025/day2/main.ts      | 78 +++++++++++++++++++++++
 3 files changed, 113 insertions(+)
 create mode 100644 src/advent-of-code/2025/day2/inputOne.txt
 create mode 100644 src/advent-of-code/2025/day2/main.spec.ts
 create mode 100644 src/advent-of-code/2025/day2/main.ts

diff --git a/src/advent-of-code/2025/day2/inputOne.txt b/src/advent-of-code/2025/day2/inputOne.txt
new file mode 100644
index 0000000..76abbd8
--- /dev/null
+++ b/src/advent-of-code/2025/day2/inputOne.txt
@@ -0,0 +1 @@
+19391-47353,9354357-9434558,4646427538-4646497433,273-830,612658-674925,6639011-6699773,4426384-4463095,527495356-527575097,22323258-22422396,412175-431622,492524-611114,77-122,992964846-993029776,165081-338962,925961-994113,7967153617-7967231799,71518058-71542434,64164836-64292066,4495586-4655083,2-17,432139-454960,4645-14066,6073872-6232058,9999984021-10000017929,704216-909374,48425929-48543963,52767-94156,26-76,1252-3919,123-228
\ No newline at end of file
diff --git a/src/advent-of-code/2025/day2/main.spec.ts b/src/advent-of-code/2025/day2/main.spec.ts
new file mode 100644
index 0000000..16ffa20
--- /dev/null
+++ b/src/advent-of-code/2025/day2/main.spec.ts
@@ -0,0 +1,34 @@
+/**
+ * @copyright NHCarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import { describe, it, expect } from "vitest";
+import { partOne, partTwo } from "./main.js";
+
+const inputOne = `11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124`;
+
+describe("partOne", () => {
+  it("should return the correct result", async() => {
+    expect(partOne(inputOne)).toBe(1_227_775_554);
+    const bigInput = await readFile(
+      join(import.meta.dirname, "inputOne.txt"),
+      "utf8",
+    );
+    expect(partOne(bigInput)).toBe(24_747_430_309);
+  });
+});
+
+describe("partTwo", () => {
+  it("should return the correct result", async() => {
+    expect(partTwo(inputOne)).toBe(4_174_379_265);
+    const bigInput = await readFile(
+      join(import.meta.dirname, "inputOne.txt"),
+      "utf8",
+    );
+    expect(partTwo(bigInput)).toBe(30_962_646_823);
+  });
+});
diff --git a/src/advent-of-code/2025/day2/main.ts b/src/advent-of-code/2025/day2/main.ts
new file mode 100644
index 0000000..bf07479
--- /dev/null
+++ b/src/advent-of-code/2025/day2/main.ts
@@ -0,0 +1,78 @@
+/**
+ * @copyright NHCarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+
+/**
+ * Determine the sum of invalid IDs in a range.
+ * An ID is invalid if it consists of two pairs of repeating digits.
+ * @param start - The start of the range.
+ * @param end - The end of the range.
+ * @returns The sum of invalid IDs in the range.
+ * @example 998-1012 has one invalid ID, 1010.
+ * @example 1188511880-1188511890 has one invalid ID, 1188511888.
+ */
+const sumInvalidIds = (start: number, end: number): number => {
+  let sum = 0;
+  for (let index = start; index <= end; index = index + 1) {
+    const id = index.toString();
+    const { length } = id;
+    if (length % 2 !== 0) {
+      continue;
+    }
+    const half = length / 2;
+    const firstHalf = id.slice(0, half);
+    const secondHalf = id.slice(half);
+    if (firstHalf === secondHalf) {
+      sum = sum + index;
+    }
+  }
+  return sum;
+};
+
+const sumLongerInvalidIds = (start: number, end: number): number => {
+  let sum = 0;
+  for (let index = start; index <= end; index = index + 1) {
+    const id = index.toString();
+    // Regex to detect if string consists ONLY of two or more groups of repeated digits, like 121212.
+    if (/^(?<name>[\d\s]+)\1+$/.test(id)) {
+      sum = sum + index;
+    }
+  }
+  return sum;
+};
+
+/**
+ * Part one of the Advent of Code 2025 day 2 challenge.
+ * @param input - The input string.
+ * @returns The sum of invalid IDs.
+ * @see https://adventofcode.com/2025/day/2
+ */
+const partOne = (input: string): number => {
+  const idRanges: Array<[number, number]> = input.split(",").map((range) => {
+    // eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- We know the input is valid.
+    return range.split("-").map(Number) as [number, number];
+  });
+  return idRanges.reduce((sum, [ start, end ]) => {
+    return sum + sumInvalidIds(start, end);
+  }, 0);
+};
+
+/**
+ * Part two of the Advent of Code 2025 day 1 challenge.
+ * @param input - The input string.
+ * @returns The number of times the position passed through 0.
+ * @see https://adventofcode.com/2025/day/1
+ */
+const partTwo = (input: string): number => {
+  const idRanges: Array<[number, number]> = input.split(",").map((range) => {
+    // eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- We know the input is valid.
+    return range.split("-").map(Number) as [number, number];
+  });
+  return idRanges.reduce((sum, [ start, end ]) => {
+    return sum + sumLongerInvalidIds(start, end);
+  }, 0);
+};
+
+export { partOne, partTwo };