93 lines
2.4 KiB
Nix
93 lines
2.4 KiB
Nix
{ pkgs, lib, AoCLib, ... }:
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with lib;
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let
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inherit (AoCLib) scanl abs repeat cmp;
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mapDirectionStepsToHorizontalVertical = { direction, steps }: {
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horizontal = if direction == "L" then steps else
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if direction == "R" then -steps else 0;
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vertical = if direction == "D" then steps else
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if direction == "U" then -steps else 0;
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};
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foldHeadPosition =
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{ x ? 0, y ? 0 }:
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{ horizontal, vertical }: {
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x = x + horizontal;
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y = y + vertical;
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};
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movements = pipe ./input.txt [
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fileContents
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(splitString "\n")
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(map (splitString " "))
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(map (x: { direction = head x; steps = toInt (elemAt x 1); }))
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(map mapDirectionStepsToHorizontalVertical)
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(scanl foldHeadPosition {})
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];
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ropePieceLength = headPiece: tailPiece: let
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deltaX = abs (headPiece.x - tailPiece.x);
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deltaY = abs (headPiece.y - tailPiece.y);
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in max deltaX deltaY;
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moveRopePiece = headPiece: tailPiece: {
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x = tailPiece.x + (cmp headPiece.x tailPiece.x);
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y = tailPiece.y + (cmp headPiece.y tailPiece.y);
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};
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moveRope = headToOverlap: rope: let
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newHead = moveRopePiece headToOverlap (head rope);
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moveIfNextPieceMoved = x: y:
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if ropePieceLength x y > 1
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then moveRopePiece x y
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else y;
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newTail = scanl moveIfNextPieceMoved newHead (tail rope);
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in [newHead] ++ newTail;
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moveRopeUntilHeadOverlapsAndReportLastPositions = headToOverlap: rope: let
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newRope = moveRope headToOverlap rope;
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nextIteration = moveRopeUntilHeadOverlapsAndReportLastPositions headToOverlap newRope;
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in if head rope == headToOverlap
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then {
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inherit rope;
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tailPositions = [];
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}
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else {
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inherit (nextIteration) rope;
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tailPositions = [(last newRope)] ++ nextIteration.tailPositions;
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};
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f = n: { rope ? (repeat { x = 0; y = 0; } n), tailPositions ? [{ x = 0; y = 0; }] }: newHeadPosition: let
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newRope = moveRopeUntilHeadOverlapsAndReportLastPositions newHeadPosition rope;
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in {
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rope = newRope.rope;
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tailPositions = tailPositions ++ newRope.tailPositions;
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};
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answer1 = pipe movements [
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(foldl (f 2) {})
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(x: x.tailPositions)
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unique
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length
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toString
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];
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answer2 = pipe movements [
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(foldl (f 10) {})
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(x: x.tailPositions)
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unique
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length
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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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