6 votes

Day 19: Tractor Beam

Automatically posted (edited )
Tags: advent of code.2019

Today's problem description: https://adventofcode.com/2019/day/19

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Please post your solutions in your own top-level comment. Here's a template you can copy-paste into your comment to format it nicely, with the code collapsed by default inside an expandable section with syntax highlighting (you can replace python with any of the "short names" listed in this page of supported languages):

<details>
<summary>Part 1</summary>

```python
Your code here.
```

</details>

1 comment

  1. Crespyl
    Link
    I needed a breather after that last one, which I barely finished in time for Day 19. With a working Intcode VM this is pretty straightforward. Part 1 This works exactly the way you'd expect, just...

    I needed a breather after that last one, which I barely finished in time for Day 19. With a working Intcode VM this is pretty straightforward.

    Part 1

    This works exactly the way you'd expect, just run a loop over the 50x50 grid and test each point in turn, counting up the hits as we go. One important detail is that each "drone" is an independent unit, they only accept one target destination and you have to "send a new drone" (clone or reset) your device before testing the next point.

    #!/usr/bin/env crystal

require "../lib/vm2.cr"
require "../lib/utils.cr"


prog = Utils.get_input_file(Utils.cli_param_or_default(0,"day19/input.txt"))
vm = VM2.from_string(prog)

hits = 0
(0...50).each do |x|
  (0...50).each do |y|
    hit = check_point(x,y,vm.clone)
    hits += hit

    if hit > 0
      print '#'
    else
      print '.'
    end
  end
  print '\n'
end

puts "Part 1: %i" % hits

def check_point(x,y,drone)
  drone.send_input(x)
  drone.send_input(y)
  drone.run
  return drone.read_output || 0
end
    Part 2 I spent a few minutes trying to figure out if there was some way to use the drones to take enough measurements for a clever triangulation solution, but that was taking too long so I reverted to a simple iterative check.

    I start out with a 100x100 box that overlaps the start of the beam, then keep scooting it right and down until the whole thing just barely fits. The only difficulty here is making sure that the output is actually the north-west corner of the box, not the south-west corner that I was basing my tests off of.

    x,y = 0,50
while true
  while check_point(x,y,vm.clone) == 0
    x += 1
  end

  if check_point(x+99,y-99,vm.clone) > 0 &&
     check_point(x+99,y,vm.clone) > 0 &&
     check_point(x,y-99,vm.clone) > 0 &&
     check_point(x,y,vm.clone) > 0
    # puts "hit at #{x},#{y}"
    break
  end

  y += 1
end

# adjust to nw corner
puts "Part 2: %i" % [x*10000 + y-99]
    1 vote