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Day 25

Executing this code

If you have a lisp installation, emacs, org-mode, and org-babel support for lisp installed you can run this by:

  1. Starting slime (M-x slime)
  2. Typing C-c C-c in the block initialize.
  3. In the repl type (in-package :aoc-2020-25)
  4. Typing C-c C-c in the block answers

Initial stuffs

Packages to load

(unless (find-package :cl-ppcre)
  (ql:quickload "cl-ppcre"))
(unless (find-package :iterate)
  (ql:quickload "iterate"))
(unless (find-package :parseq)
  (ql:quickload "parseq"))
(unless (find-package :fiveam)
  (ql:quickload "fiveam"))
(unless (find-package :series)
  (ql:quickload "series"))
(unless (find-package :cl-permutation)
  (ql:quickload "cl-permutation"))
(unless (find-package :bordeaux-threads)
  (ql:quickload "bordeaux-threads"))

Create package for this day

<<packages>>
(defpackage :aoc-2020-25
  (:use :common-lisp
        :iterate
        :parseq
        :fiveam)
  (:export :problem-a
           :problem-b))
(in-package :aoc-2020-25)

Input

(defun read-input (file)
  (iter (for line in-file file using #'read-line)
        (collect (parse-integer line))))
(defparameter *input*
  (read-input "input/25.txt"))

Part 1

Breaking the cryptographic security of a hotel room door.

(defparameter *magic* 20201227)
(defun find-loop-size (n)
  (loop for i from 0
     with subject-number = 7
     for value = 1 then (mod (* value subject-number) *magic*)
     until (= value n)
     finally (return i)))
(defun find-encryption-key (subject-number loop-size)
  (loop repeat loop-size
     for value = subject-number then (mod (* value subject-number) *magic*)
     finally (return value)))
(defun problem-a () (format t "Problem 25 A: ~a~%" (find-encryption-key (first *input*) (find-loop-size (second *input*)))))

Part 2

(defun problem-b () (format t "Problem 25 B: ~a~%" "free star!"))

Putting it all together



<<read-input>>
<<input>>


<<initialize>>
<<structs>>
<<functions>>
<<input>>
<<problem-a>>
<<problem-b>>
(problem-a)
(problem-b)


Answer


Problem 25 A: 6408263
Problem 25 B: free star!



Test Cases


(def-suite aoc.2020.25)
(in-suite aoc.2020.25)
(test loop-size
  (is (= 8 (find-loop-size 5764801)))
  (is (= 11 (find-loop-size 17807724))))
(test encryption-key
  (is (= 14897079 (find-encryption-key 17807724 8)))
  (is (= 14897079 (find-encryption-key 5764801 11))))
(run! 'aoc.2020.25)


Test Results


Running test suite AOC.2020.25
 Running test LOOP-SIZE ..
 Running test ENCRYPTION-KEY ..
 Did 4 checks.
    Pass: 4 (100%)
    Skip: 0 ( 0%)
    Fail: 0 ( 0%)



Thoughts


Ada


Runner


Simple runner.


with AOC2020.Day25;
procedure Day25 is
begin
  AOC2020.Day25.Run;
end Day25;


Specification


Specification for solution.


package AOC2020.Day25 is
   procedure Run;
end AOC2020.Day25;


Packages


with GNAT.Regpat; use GNAT.Regpat;
with Text_IO; use Text_IO;


Types and generics




Implementation


Actual implementation body.


<<ada-packages>>
package body AOC2020.Day25 is
   <<types-and-generics>>
   -- Used as an example of matching regular expressions
   procedure Parse_Line (Line : Unbounded_String; P : out Password) is
      Pattern : constant String := "(\d+)-(\d+) ([a-z]): ([a-z]+)";
      Re : constant Pattern_Matcher := Compile(Pattern);
      Matches : Match_Array (0..4);
      Pass : Unbounded_String;
      P0, P1 : Positive;
      C : Character;
   begin
      Match(Re, To_String(Line), Matches);
      P0 := Integer'Value(Slice(Line, Matches(1).First, Matches(1).Last));
      P1 := Integer'Value(Slice(Line, Matches(2).First, Matches(2).Last));
      C := Element(Line, Matches(3).First);
      Pass := To_Unbounded_String(Slice(Line, Matches(4).First, Matches(4).Last));
      P := (Min_Or_Pos => P0,
            Max_Or_Pos => P1,
            C => C,
            P => Pass);
   end Parse_Line;
   procedure Run is
   begin
      Put_Line("Advent of Code 2020 - Day 25");
      Put_Line("The result for Part 1 is " & Integer'Image(0));
      Put_Line("The result for Part 2 is " & Integer'Image(0));
   end Run;
end AOC2020.Day25;


Run the program


In order to run this you have to “tangle” the code first using C-c
  C-v C-t.


cd ada
gnatmake day25
./day25