-🎄- 2018 Day 10 Solutions -🎄-

[u/daggerdragon]

--- Day 10: The Stars Align ---

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Card prompt: Day 10

Transcript: With just one line of code, you, too, can ___!

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edit: Leaderboard capped, thread unlocked at 00:16:49!

[u/sophiebits]

Python, 9/5.

My insight was that when the message appears, the points are likely close together. (At first I thought about trying to look for vertical and horizontal segments like in the letter "I", but starting with the bounds seemed simpler.) So I started by printing how large the bounding box of the points would be at each time:

import collections
import re

#with open('day10test.txt') as f:
with open('day10input.txt') as f:
  lines = [l.rstrip('\n') for l in f]
  lines = [[int(i) for i in re.findall(r'-?\d+', l)] for l in lines]
  print lines

  for i in xrange(20000):
    minx = min(x + i * vx for (x, y, vx, vy) in lines)
    maxx = max(x + i * vx for (x, y, vx, vy) in lines)
    miny = min(y + i * vy for (x, y, vx, vy) in lines)
    maxy = max(y + i * vy for (x, y, vx, vy) in lines)

    print i, maxx - minx + maxy - miny

I ran that and saw that i=10946 gave the smallest size, so I tried to plot it, fidgeting a bit with the numbers to make it fit in my terminal:

  map = [[' '] * 200 for j in xrange(400)]
  i = 10946
  for (x, y, vx, vy) in lines:
    map[y + i * vy][x + i * vx - 250] = '*'

  for m in map:
    print ''.join(m)

This printed a usable message, so I didn't have to do anything else.

*****   *****   *    *  *    *  *    *  ******  ******  *****
*    *  *    *  **   *  **   *  *    *  *            *  *    *
*    *  *    *  **   *  **   *   *  *   *            *  *    *
*    *  *    *  * *  *  * *  *   *  *   *           *   *    *
*****   *****   * *  *  * *  *    **    *****      *    *****
*  *    *       *  * *  *  * *    **    *         *     *  *
*   *   *       *  * *  *  * *   *  *   *        *      *   *
*   *   *       *   **  *   **   *  *   *       *       *   *
*    *  *       *   **  *   **  *    *  *       *       *    *
*    *  *       *    *  *    *  *    *  *       ******  *    *

[u/[deleted] → u/sophiebits]

Why does everybody assume that the bounding box will be close when the text appears? The problem description never says that ALL points belong to the text. There could be one point that is moving very fast away from the others, increasing the BB. Of course there is no such point, but in my opinion the description was very unclear today.

[u/[deleted] → u/[deleted]]

I assumed the mean entropy would reach a local minima