Grimmauld/Advent-of-Nix-2024
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alternative day 2 solution: zipListsWith for deltas, just two checks

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Grimmauld 2024-12-02 22:36:05 +01:00
parent 315d8a4aa3
commit ff7f326e1d
Signed by: Grimmauld
SSH key fingerprint: SHA256:Q8IL6Y7sSKqzkyFdV1L0O/EflEh1fFV3tBtwxpapRH4
2 changed files with 5 additions and 13 deletions
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17
day2/default.nix
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@ -4,20 +4,11 @@ with builtins;
with utils;
let
records = map (l: map toInt (splitWhitespace l)) (readLines ./input);
getMaxDelta = l:
(foldl' (prev: value: {
inherit value;
maxDelta = max prev.maxDelta (delta prev.value value);
}) {
value = head l;
maxDelta = 0;
} l).maxDelta;
getDeltas = r: zipListsWith sub (init r) (drop 1 r);
isSafe = r:
let sorted = sort lessThan r;
in (r == sorted || r == (reverseList sorted)) && allUnique r
&& (3 >= getMaxDelta r);
isSafeDampened = r:
any isSafe ([ r ] ++ (map (deleteAt r) (range 0 (length r))));
let deltas = getDeltas r;
in (all (d: -3 <= d && d < 0) deltas) || (all (d: 3 >= d && d > 0) deltas);
isSafeDampened = r: any isSafe (map (deleteAt r) (listRange r));
in {
part1 = count isSafe records;
part2 = count isSafeDampened records;

1
utils.nix
View file

@ -9,4 +9,5 @@ with builtins; rec {
deleteAt = l: i: (take i l) ++ (drop (i + 1) l);
eq = x: y: x == y;
greaterThan = x: y: x > y;
listRange = l: range 0 (length l);
}