Inverse Captcha

Advent of Code 2017 Day 1

Part 1

1. Circular lists from the beginning!
2. Writing my working algorithm

Circular lists from the beginning!

• I knew it was a recurring theme throughout the year
• But I didn't know it started with Day 1

Writing my working algorithm

An outline of my algorithm

Split the input into an array of numbers
For each number
  Accumulate a sum, starting a 0
    If the next number (wrapping if necessary) is the same number
      Increment the sum by the number at the current index
    Otherwise, increment the sum by 0...leaving it unchanged

A reduce() that leverages all of the possible parameters:

return input
  .split('')
  .map(Number)
  .reduce((acc, curr, index, RA) =>
    acc += RA[index] == RA[(index + 1) % RA.length]
        ? curr : 0
  , 0)

Part 2

Adjusting my working algorithm

Instead of checking the next index, I'll check the index half a list away.

An outline of my algorithm

Split the input into an array of numbers
For each number
  Accumulate a sum, starting a 0
    If the number half a list length away (wrapping if necessary) is the same number
      Increment the sum by the number at the current index
    Otherwise, increment the sum by 0...leaving it unchanged

A small tweak to the number being added to index, and Voila!

return input
  .split('')
  .map(Number)
  .reduce((acc, curr, index, RA) =>
    acc += RA[index] == RA[(index + (RA.length / 2)) % RA.length]
        ? curr : 0
  , 0)

I did it!!

• I solved both parts!
• Using one long statement comprised of chained array methods!
• Where both parts only differ by a single operand!

Year in review

Since I worked in reverse, today was the first time I saw this animation:

This static map should which puzzles I made simulators for:

• 46 stars! A new personal best!
• 21 two-star days! A new personal best!
• 4 one-star days! A new personal best!
• 0 no-star days! A new personal best!
• 8 simulators built! A tie with 2018 for lowest amount.
• Tons of GIFs created...many which helped me solve the puzzle!

It's been a blast, 2017!