/**
 * Solver for Day 2 of Advent of Code 2025
 *
 * To use this solver:
 * 1. Implement the solve function below
 * 2. The function receives the puzzle input as a string
 * 3. Return the solution (can be a string, number, or object)
 */

const isInvalidPt1 = (number: number): boolean => {
  const numberStr = number.toString()
  const firstHalf = numberStr.slice(0, numberStr.length / 2)
  const secondHalf = numberStr.slice(numberStr.length / 2)
  if (firstHalf === secondHalf) {
    return true
  }
  return false
}

const isInvalidPt2 = (number: number): boolean => {
  const numberStr = number.toString()
  const len = numberStr.length
  const half = Math.floor(len / 2)
  for (let idx = 1; idx <= half; idx++) {
    if (len % idx !== 0) {
      continue
    }
    const repeat = len / idx
    if (repeat < 2) {
      continue
    }
    const sub = numberStr.slice(0, idx)
    const repeated = sub.repeat(repeat)
    if (numberStr === repeated) {
      return true
    }
  }
  return false
}

export function solve(input: string): Promise<string | number | object> {
  const ranges = input.split(',')
  let countPt1 = 0
  let countPt2 = 0
  for (const range of ranges) {
    const [startStr, endStr] = range.split('-')
    const start = parseInt(startStr)
    const end = parseInt(endStr)
    for (let num = start; num <= end; num++) {
      if (isInvalidPt1(num)) {
        countPt1 += num
      }
      if (isInvalidPt2(num)) {
        countPt2 += num
      }
    }
  }
  return Promise.resolve({
    part1: countPt1,
    part2: countPt2,
  })
}

export async function solve(input: string): Promise<string | number | object> {
  // Your solution here
  // The input parameter contains the puzzle input as a string
  
  // Example:
  const lines = input.trim().split('\n');
  
  // Process and return your answer
  return 'Your answer here';
}

import * as day02 from './day02'

export const solvers = {
  // ... existing solvers
  '02': day02,
}

--- Day 2: Gift Shop ---

You get inside and take the elevator to its only other stop: the gift shop. "Thank you for visiting the North Pole!" gleefully exclaims a nearby sign. You aren't sure who is even allowed to visit the North Pole, but you know you can access the lobby through here, and from there you can access the rest of the North Pole base.

As you make your way through the surprisingly extensive selection, one of the clerks recognizes you and asks for your help.

As it turns out, one of the younger Elves was playing on a gift shop computer and managed to add a whole bunch of invalid product IDs to their gift shop database! Surely, it would be no trouble for you to identify the invalid product IDs for them, right?

They've even checked most of the product ID ranges already; they only have a few product ID ranges (your puzzle input) that you'll need to check. For example:

11-22,95-115,998-1012,1188511880-1188511890,222220-222224,
1698522-1698528,446443-446449,38593856-38593862,565653-565659,
824824821-824824827,2121212118-2121212124

(The ID ranges are wrapped here for legibility; in your input, they appear on a single long line.)

The ranges are separated by commas (,); each range gives its first ID and last ID separated by a dash (-).

Since the young Elf was just doing silly patterns, you can find the invalid IDs by looking for any ID which is made only of some sequence of digits repeated twice. So, 55 (5 twice), 6464 (64 twice), and 123123 (123 twice) would all be invalid IDs.

None of the numbers have leading zeroes; 0101 isn't an ID at all. (101 is a valid ID that you would ignore.)

Your job is to find all of the invalid IDs that appear in the given ranges. In the above example:

• 11-22 has two invalid IDs, *11* and *22*.
• 95-115 has one invalid ID, *99*.
• 998-1012 has one invalid ID, *1010*.
• 1188511880-1188511890 has one invalid ID, *1188511885*.
• 222220-222224 has one invalid ID, *222222*.
• 1698522-1698528 contains no invalid IDs.
• 446443-446449 has one invalid ID, *446446*.
• 38593856-38593862 has one invalid ID, *38593859*.
• The rest of the ranges contain no invalid IDs.

Adding up all the invalid IDs in this example produces *1227775554*.

What do you get if you add up all of the invalid IDs?

Your puzzle answer was 24747430309.

The first half of this puzzle is complete! It provides one gold star: *

--- Part Two ---

The clerk quickly discovers that there are still invalid IDs in the ranges in your list. Maybe the young Elf was doing other silly patterns as well?

Now, an ID is invalid if it is made only of some sequence of digits repeated at least twice. So, 12341234 (1234 two times), 123123123 (123 three times), 1212121212 (12 five times), and 1111111 (1 seven times) are all invalid IDs.

From the same example as before:

• 11-22 still has two invalid IDs, *11* and *22*.
• 95-115 now has two invalid IDs, *99* and *111*.
• 998-1012 now has two invalid IDs, *999* and *1010*.
• 1188511880-1188511890 still has one invalid ID, *1188511885*.
• 222220-222224 still has one invalid ID, *222222*.
• 1698522-1698528 still contains no invalid IDs.
• 446443-446449 still has one invalid ID, *446446*.
• 38593856-38593862 still has one invalid ID, *38593859*.
• 565653-565659 now has one invalid ID, *565656*.
• 824824821-824824827 now has one invalid ID, *824824824*.
• 2121212118-2121212124 now has one invalid ID, *2121212121*.

Adding up all the invalid IDs in this example produces *4174379265*.

What do you get if you add up all of the invalid IDs using these new rules?

Answer:

Although it hasn't changed, you can still get your puzzle input.

You can also [Shareon Bluesky Twitter Mastodon] this puzzle.