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Discussion on: Advent of Code 2019 Solution Megathread - Day 4: Secure Container

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Neil Gall • • Edited

Back in the early 1990s in my CS degree we did a genetic algorithm polynomial solver in Prolog. My Prolog has become a bit rusty through disuse since then but I was hoping for a constraint solving problem to dust it off.

Later I might try again using one of my MiniKanren implementations (e.g. github.com/neilgall/KotlinKanren)

digit(0).
digit(1).
digit(2).
digit(3).
digit(4).
digit(5).
digit(6).
digit(7).
digit(8).
digit(9).

in_range(Min, Max, A, B, C, D, E, F) :-
     X = (((((A * 10 + B) * 10 + C) * 10) + D) * 10 + E) * 10 + F
   , Min =< X
   , X =< Max.

has_adjacent_digits_the_same(A, B, C, D, E, F) :-
      A == B
    ; B == C
    ; C == D
    ; D == E
    ; E == F.

adjacent_digits_not_in_larger_group(A, B, C, D, E, F) :-
              A == B, B \= C
    ; A \= B, B == C, C \= D
    ; B \= D, C == D, D \= E
    ; C \= E, D == E, E \= F
    ; D \= E, E == F.

has_no_decreasing_digits(A, B, C, D, E, F) :-
      A =< B
    , B =< C
    , C =< D
    , D =< E
    , E =< F.

solve_part1(Min, Max, A, B, C, D, E, F) :-
      digit(A)
    , digit(B)
    , digit(C)
    , digit(D)
    , digit(E)
    , digit(F)
    , has_adjacent_digits_the_same(A, B, C, D, E, F)
    , has_no_decreasing_digits(A, B, C, D, E, F)
    , in_range(Min, Max, A, B, C, D, E, F).

solve_part2(Min, Max, A, B, C, D, E, F) :-
      solve_part1(Min, Max, A, B, C, D, E, F)
    , adjacent_digits_not_in_larger_group(A, B, C, D, E, F).

part1(Min, Max, Count) :-
      setof([A, B, C, D, E, F], solve_part1(Min, Max, A, B, C, D, E, F), Set)
    , length(Set, Count).

part2(Min, Max, Count) :-
      setof([A, B, C, D, E, F], solve_part2(Min, Max, A, B, C, D, E, F), Set)
    , length(Set, Count).