99 lines
2.8 KiB
Nix
99 lines
2.8 KiB
Nix
{ pkgs, lib }:
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with lib;
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let
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# See https://github.com/NixOS/nixpkgs/pull/205457
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toInt = str:
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let
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inherit (builtins) match fromJSON;
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# RegEx: Match any leading whitespace, possibly a '-', one or more digits,
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# and finally match any trailing whitespace.
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strippedInput = match "[[:space:]]*(-?[[:digit:]]+)[[:space:]]*" str;
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# RegEx: Match a leading '0' then one or more digits.
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isLeadingZero = match "0[[:digit:]]+" (head strippedInput) == [];
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# Attempt to parse input
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parsedInput = fromJSON (head strippedInput);
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generalError = "toInt: Could not convert ${escapeNixString str} to int.";
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octalAmbigError = "toInt: Ambiguity in interpretation of ${escapeNixString str}"
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+ " between octal and zero padded integer.";
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in
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# Error on presence of non digit characters.
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if strippedInput == null
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then throw generalError
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# Error on presence of leading zero/octal ambiguity.
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else if isLeadingZero
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then throw octalAmbigError
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# Error if parse function fails.
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else if !isInt parsedInput
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then throw generalError
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# Return result.
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else parsedInput;
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lineToInstruction = line:
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if line == "noop"
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then { type = "n"; }
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else { type = "a"; val = toInt (elemAt (splitString " " line) 1); };
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foldToSignalState = { cycles ? 0, X ? 0, nextX ? 1 }: instructions: let
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instr = head instructions;
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nextSignalState = if instr.type == "n"
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then { cycles = 1; X = nextX; inherit nextX; }
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# Implicit `addx`
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else { cycles = 2; X = nextX; nextX = nextX + instr.val; };
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in if instructions == [] then [] else [nextSignalState] ++ (foldToSignalState nextSignalState (tail instructions));
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repeat = item: times: map (const item) (range 1 times);
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expandSignalStates = signalStates: let
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s = head signalStates;
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in if signalStates == []
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then []
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else (repeat s.X s.cycles) ++ (expandSignalStates (tail signalStates));
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takeWithStride = n: l:
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if l == [] then [] else [(head l)] ++ takeWithStride n (drop n l);
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signalStates = pipe ./input.txt [
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fileContents
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(splitString "\n")
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(map lineToInstruction)
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(foldToSignalState {})
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expandSignalStates
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];
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answer1 = pipe signalStates [
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(imap1 (i: v: i * v))
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(drop 19)
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(takeWithStride 40)
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(foldr add 0)
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toString
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];
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splitAtInterval = n: list:
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if list == [] then []
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else [(take n list)] ++ (splitAtInterval n (drop n list));
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f = i: v: if v <= i && i <= v + 2 then "#" else ".";
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answer2 = pipe signalStates [
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(splitAtInterval 40)
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(map (imap1 f))
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(map (concatStringsSep ""))
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(concatStringsSep "\n")
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toString
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];
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in pkgs.writeText "answers" ''
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Task1:
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${answer1}
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Task2:
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${answer2}
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''
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