Day 8
Al lot of grid index shuffling these past few days! Not too difficult yet though, will this year be gentler or much harsher later?
Part 2 code in JQ
#!/usr/bin/env jq -n -R -f
[ inputs / "" ] | [.,.[0]|length] as [$H,$W] |
#----- In bound selectors -----#
def x: select(. >= 0 and . < $W);
def y: select(. >= 0 and . < $H);
reduce (
[
to_entries[] | .key as $y | .value |
to_entries[] | .key as $x | .value |
[ [$x,$y],. ] | select(last!=".")
] | group_by(last)[] # Every antenna pair #
| combinations(2) | select(first < last)
) as [[[$ax,$ay]],[[$bx,$by]]] ({};
# Assign linear anti-nodes #
.[ range(-$H;$H) as $i | "\(
[($ax+$i*($ax-$bx)|x), ($ay+$i*($ay-$by)|y)] | select(length==2)
)"] = true
) | length
Day 9 discussion
Part two for me was also very slow until I, speed up the index search by providing a lower bound for the insertion. for every insertion of size "N", I have an array lower = [null, 12, 36, ...], since from the left any time you find free space for a given size, the next time must be at an index at least one larger, which makes it close to being O(N) [assuming search for the next free space is more or less constant] instead of O(N^2), went from about 30s to 2s. https://github.com/zogwarg/advent-of-code/blob/main/2024/jq/09-b.jq