aoc2021/pl/05.1.pl

parse_line(S, [A, B, C, D]) :-
    split_string(S, " ->", "", [X, _, _, _, Y]),
    split_string(X, ",", "", [A0, B0]),
    split_string(Y, ",", "", [C0, D0]),
    number_string(A, A0),
    number_string(B, B0),
    number_string(C, C0),
    number_string(D, D0).

read_file(Stream, []) :-
    at_end_of_stream(Stream).
read_file(Stream, [X|L]) :-
    \+ at_end_of_stream(Stream),
    read_line_to_codes(Stream, C),
    string_chars(S, C),
    parse_line(S, X),
    read_file(Stream, L).

main :-
    open('../input/05', read, Stream),
    read_file(Stream, Lines), !,
    close(Stream),
    minmax_seq(Lines, X0, X1, Y0, Y1),
    C = [X0 - 10, X1 + 10, Y0 - 10, Y1 + 10],
    filter_hor_vert(Lines, L0),
    convert_coords(L0, C, L1),
    create_grid(C, G), !,
    mark_lines(G, L1, G1), !,
    count_ge2(G1, W),
    print(W).

filter_hor_vert([], []).
filter_hor_vert([A|As], [A|Bs]) :-
    (horizontal(A); vertical(A)),
    filter_hor_vert(As, Bs).
filter_hor_vert([A|As], B) :-
    \+ horizontal(A),
    \+ vertical(A),
    filter_hor_vert(As, B).

convert_coords([], _, []).
convert_coords([[A0,A1,A2,A3]|As], [X0, X1, Y0, Y1], [[B0,B1,B2,B3]|Bs]) :-
    C0 is A0 - X0,
    C1 is A1 - Y0,
    C2 is A2 - X0,
    C3 is A3 - Y0,
    B0 is min(C0, C2),
    B2 is max(C0, C2),
    B1 is min(C1, C3),
    B3 is max(C1, C3),
    convert_coords(As, [X0, X1, Y0, Y1], Bs).

create_row(0, []).
create_row(X, [0|As]) :-
    X > 0,
    X1 is X - 1,
    create_row(X1, As).
create_grid([X0, X1, Y0, Y1], A) :-
    create_grid(X1 - X0 + 1, Y1 - Y0 + 1, A).
create_grid(_, 0, []).
create_grid(X, Y, [A|As]) :-
    Y > 0,
    Y1 is Y - 1,
    create_row(X, A),
    create_grid(X, Y1, As).

minmax([A, B, C, D], X0, X1, Y0, Y1) :-
    X0 is min(A, C),
    X1 is max(A, C),
    Y0 is min(B, D),
    Y1 is max(B, D).

minmax_seq([A], X0, X1, Y0, Y1) :-
    minmax(A, X0, X1, Y0, Y1).
minmax_seq([A|As], X0, X1, Y0, Y1) :-
    minmax_seq(As, X00, X01, Y00, Y01),
    minmax(A, X10, X11, Y10, Y11),
    X0 is min(X00, X10),
    X1 is max(X01, X11),
    Y0 is min(Y00, Y10),
    Y1 is max(Y01, Y11).

vertical([A, _, A, _]).
horizontal([_, A, _, A]).

prefix_n(0, _, []).
prefix_n(X, [A|As], [A|Ps]) :-
    X > 0,
    X1 is X - 1,
    prefix_n(X1, As, Ps), !.

suffix_n(N, A, S) :-
    reverse(A, B),
    prefix_n(N, B, P),
    reverse(P, S), !.

add_one([], []).
add_one([A|As], [B|Bs]) :-
    B is A + 1,
    add_one(As, Bs), !.

mark_in_row(X, [A, B], Y) :-
    length(X, L),
    L1 is L - B - 1,
    prefix_n(A, X, Pfx),
    suffix_n(L1, X, Sfx),
    append([Pfx, Q, Sfx], X),
    add_one(Q, W),
    append([Pfx, W, Sfx], Y), !.

mark_row(X, [A, B, C, B], Y) :-
    length(X, L),
    L1 is L - B - 1,
    prefix_n(B, X, Pfx),
    suffix_n(L1, X, Sfx),
    nth0(B, X, Row0),
    mark_in_row(Row0, [A, C], Row1),
    append([Pfx, [Row1], Sfx], Y), !.

mark_cols([], _, []).
mark_cols([X|Xs], A, [Y|Ys]) :-
    mark_in_row(X, [A, A], Y), !,
    mark_cols(Xs, A, Ys), !.
mark_col(X, [A, B, A, D], Y) :-
    length(X, L),
    L1 is L - D - 1,
    prefix_n(B, X, Pfx),
    suffix_n(L1, X, Sfx),
    append([Pfx, Q, Sfx], X),
    mark_cols(Q, A, W), !,
    append([Pfx, W, Sfx], Y).

mark_line(X, Z, Y) :-
    (mark_col(X, Z, Y), !); (mark_row(X, Z, Y), !).

mark_lines(X, [], X).
mark_lines(X, [Z|Zs], Y) :-
    mark_line(X, Z, Y0), !,
    mark_lines(Y0, Zs, Y), !.

count_ge2_row([], 0).
count_ge2_row([A|As], C) :-
    A >= 2,
    count_ge2_row(As, C1),
    C is C1 + 1.
count_ge2_row([A|As], C) :-
    A < 2,
    count_ge2_row(As, C).
count_ge2([], 0).
count_ge2([X|Xs], Y) :-
    count_ge2(Xs, Y0),
    count_ge2_row(X, Y1),
    Y is Y0 + Y1.