I Was Told There Would Be No Math

#adventofcode #algorithms #programming #javascript

Advent of Code 2015 Day 2

Part 1

Oh, there will be plenty of math.
Using several familiar tools in my toolbox

Oh, there will be plenty of math.

Much to my delight, a majority of the math throughout Advent of Code was in celebration of patterns underlying various scientific, arithmetic or algorithmic formulas and proofs.

Using several familiar tools in my toolbox

reduce() to accumulate a total
split() to turn a string into an array
map() to coerce or manipulate data
array destructuring to concisely extract and store multiple values
sort() to, well, sort numbers
slice() to extract a subset of items from an array

My algorithm in JavaScript:

input.reduce(
  (sqft, box) => {
    let [l, w, h] = box.split('x').map(Number)
    let smallestArea = [l, w, h]
      .sort((a, b) => a - b)
      .slice(0, 2)
      .reduce((a, c) => a * c)
    return sqft += 2*l*w + 2*w*h + 2*h*l + smallestArea
  }
, 0)

Part 2

A minor mathematical tweak

A shorter equation
And a relatively unchanged algorithm

My algorithm in JavaScript:

input.reduce(
  (sqft, box) => {
    let [l, w, h] = box.split('x').map(Number)
    let smallestPerimeter = [l, w, h]
      .sort((a, b) => a - b)
      .slice(0, 2)
      .map(el => el * 2)
      .reduce((a, c) => a + c)
    return sqft += l*w*h + smallestPerimeter
  }
, 0)

Both parts, a year ago

This was my working algorithm in JavaScript when I first solved this puzzle:

function dayTwoPart1(input) {
  return input.map(box => wrappingPaperFor(box))
              .reduce((acc, curr) => { return acc + curr }, 0)
}

function dayTwoPart2(input) {
  return input.map(box => ribbonFor(box))
              .reduce((acc, curr) => { return acc + curr }, 0)
}

function wrappingPaperFor(box) {
  return surfaceAreaFor(box) + slackFor(box)
}

function surfaceAreaFor(box) {
  let [l, w, h] = box.split("x").map(i => +i)
  return (2 * l * w) + (2 * w * h) + (2 * h * l)
}

function slackFor(box) {
  let sortedBox = box.split("x").map(i => +i).sort((a,b) => a - b)
  return sortedBox[0] * sortedBox[1]
}
function ribbonFor(box) {
    let [s1, s2, s3] = box.split("x").map(i => +i).sort((a,b) => a - b)
    return (s1 + s1 + s2 + s2) + (s1 * s2 * s3)
}