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Rules: no spoilers, use the handy dandy spoiler preset to mark discussions as spoilers
Day 14, got very lucky on this one, but too tired to think about why part 2 still worked.
spoiler
#!/usr/bin/env jq -n -R -f
# Board size # Our list of robots positions and speed #
[101,103] as [$W,$H] | [ inputs | [scan("-?\\d+")|tonumber] ] |
# Making the assumption that the easter egg occurs when #
# When the quandrant product is minimized #
def sig:
reduce .[] as [$x,$y] ([];
if $x < ($W/2|floor) and $y < ($H/2|floor) then
.[0] += 1
elif $x < ($W/2|floor) and $y > ($H/2|floor) then
.[1] += 1
elif $x > ($W/2|floor) and $y < ($H/2|floor) then
.[2] += 1
elif $x > ($W/2|floor) and $y > ($H/2|floor) then
.[3] += 1
end
) | .[0] * .[1] * .[2] * .[3];
# Only checking for up to W * H seconds #
# There might be more clever things to do, to first check #
# vertical and horizontal alignement separately #
reduce range($W*$H) as $s ({ b: ., bmin: ., min: sig, smin: 0};
.b |= (map(.[2:4] as $v | .[0:2] |= (
[.,[$W,$H],$v] | transpose | map(add)
| .[0] %= $W | .[1] %= $H
)))
| (.b|sig) as $sig |
if $sig < .min then
.min = $sig | .bmin = .b | .smin = $s
end | debug($s)
)
| debug(
# Contrary to original hypothesis that the easter egg #
# happens in one of the quandrants, it occurs almost bang #
# in the center, but this is still somehow the min product #
reduce .bmin[] as [$x,$y] ([range($H)| [range($W)| " "]];
.[$y][$x] = "█"
) |
.[] | add
)
| .smin + 1 # Our easter egg step
And a bonus tree:
Pt2 commentary
I randomly got it by sorting for the most robots in the bottom left quadrant while looking for robot concentrations, it was number 13. Despite being in the centre of the grid it didn’t show up when sorting for most robots in the middle 30% columns of the screen, which is kind of wicked, in the traditional sense.
The first things I tried was looking for horizontal symmetry (find a grid where all the lines have the same number of robots on the left and on the right of the middle axis, there is none, and the tree is about a third to a quarted of the matrix on each side) and looking for grids where the number of robots increased towards the bottom of the image (didn’t work, because turns out tree is in the middle of the screen).
I thinks I was on the right track with looking for concentrations of robots, wish I’d thought about ranking the matrices according to the amount of robots lined up without gaps. Don’t know about minimizing the safety score, sorting according to that didn’t show the tree anywhere near the first tens.
Realizing that the patterns start recycling at ~10.000 iterations simplified things considerably.
The tree on the terminal output
(This is three matrices separated by rows of underscores)
Updated Reasoning
Ok it probably works because it isn’t bang center but a bit up of center, most other steps most be half half noise vertically, and the reason it doesn;t minimize on an earlier horizontal step (where every step is mostly half half), is because the middle points on the trunk, that don’t contribute to the overall product therefore minimizing it even lower.
re: day 14 part 2
I had nfc how to solve this but someoone on the subreddit mentioned that miminizine the “safety score” was the way to go too … I guess your explanation is the correct one. Also the way the puzzle is generated is to start with the tree and go “backwards” a couple of thousand steps and use a number of of those as starting positions. Probably throw in some random robots as noise.
