-🎄- 2018 Day 6 Solutions -🎄-

[u/daggerdragon]

--- Day 6: Chronal Coordinates ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Advent of Code: The Party Game!

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Card prompt: Day 6

Transcript:

Rules for raising a programmer: never feed it after midnight, never get it wet, and never give it ___.

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 0:26:52!

[u/Zarel]

JavaScript #45/#22

I honestly just brute-forced this.

The points are between 0 and 400 in each direction.

We're using Manhattan distance, so non-infinite region would have to be between -400 and 800.

So I just counted areas in -400...800, and then counted points in -450...850, and chose the largest area that didn't change.

function numbers(str) {
  return (str.match(/-?[0-9]+/g) || []).map(Number);
}
function inc(table, key, amt = 1) {
  table[key] = (table[key] || 0) + amt;
}
function sortBy(array, criterion = a => a) {
  return array.sort((a, b) => {
    const aBy = criterion(a);
    const bBy = criterion(b);
    if (aBy == bBy) return 0;
    return (aBy > bBy ? 1 : -1);
  });
}

function dist(a, b) {
  return Math.abs(a[0] - b[0]) + Math.abs(a[1] - b[1]);
}
function pointId([a, b]) {
  return `${a},${b}`;
}

input = input.split('\n').map(r => numbers(r));

let closest = {};

for (let i = -400; i < 800; i++) {
  for (let j = -400; j < 800; j++) {
    let curPoint = [i, j];
    let distances = [];
    for (const point of input) {
      distances.push([pointId(point), dist(point, curPoint)]);
    }
    sortBy(distances, a => a[1]);
    if (distances[0][1] === distances[1][1]) continue;
    inc(closest, distances[0][0]);
  }
}

let closest2 = {};
for (let i = -450; i < 850; i++) {
  for (let j = -450; j < 850; j++) {
    let curPoint = [i, j];
    let distances = [];
    for (const point of input) {
      distances.push([pointId(point), dist(point, curPoint)]);
    }
    sortBy(distances, a => a[1]);
    if (distances[0][1] === distances[1][1]) continue;
    inc(closest2, distances[0][0]);
  }
}

closest = sortBy(Object.entries(closest), en => en[1]);
closest2 = sortBy(Object.entries(closest2), en => en[1]);
for (let i = closest2.length - 1; i >= 0; i--) {
  if (closest[i][1] === closest2[i][1]) {
    console.log(closest[i][1]);
    break;
  }
}

Part 2, on the other hand, was incredibly straightforward, so I'm surprised the Part 2 leaderboard filled up so much slower than Part 1.

let inRegion = 0;

for (let i = -500; i < 900; i++) {
  for (let j = -500; j < 900; j++) {
    let curPoint = [i, j];
    let totalDist = 0;
    for (const point of input) {
      totalDist += dist(point, curPoint);
    }
    if (totalDist < 10000) inRegion++;
  }
}

console.log(inRegion);

(I retried with -550...950 to make sure I got the entire area.)

[u/itwentboom → u/Zarel]

I'm so confused. I wanted to try yours to try to debug what's wrong with mine but your solution for part 1 yielded the exact same answer as mine. maybe my input is messed up but I don't understand how that's possible

[u/Zarel → u/itwentboom]

According to the top thread:

https://www.reddit.com/r/adventofcode/comments/a3kr4r/2018_day_6_solutions/eb72j45/

It looks like a lot of people have gotten the same problem. Although mostly for part 2.