174 lines
4.4 KiB
Prolog
174 lines
4.4 KiB
Prolog
chars_digits([], []).
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chars_digits([A|As], [B|Bs]) :-
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char_type(A, digit(B)),
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chars_digits(As, Bs).
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read_file(Stream, []) :-
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at_end_of_stream(Stream).
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read_file(Stream, [X|Xs]) :-
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\+ at_end_of_stream(Stream),
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read_line_to_codes(Stream, C),
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chars_digits(C, X),
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read_file(Stream, Xs).
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main :-
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open('../input/09', read, Stream),
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read_file(Stream, Lines), !,
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close(Stream),
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low_points(Lines, Res),
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basins(Lines, Res, B0),
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msort(B0, B1),
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reverse(B1, [B2,B3,B4|_]),
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X is B2 * B3 * B4,
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print(X).
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basins(_, [], []).
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basins(A, [P|Ps], [B|Bs]) :-
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points_high_neighbors_all(A, [P], Bas),
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length(Bas, B),
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basins(A, Ps, Bs).
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low_point([[A,B|_]|[[C|_]|_]], 0, 0) :-
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A < B, A < C.
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low_point([A|As], X, 0) :-
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X > 0,
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nth0(X, A, R0),
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X0 is X - 1,
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X1 is X + 1,
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nth0(X0, A, R1),
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R0 < R1,
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(
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(length(A, X1), length([A|As], 1));
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(length([A|As], 1), nth0(X1, A, R2), R0 < R2);
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(length(A, X1), nth0(1, [A|As], E), nth0(X, E, E0), R0 < E0);
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(nth0(X1, A, R2), R0 < R2, nth0(1, [A|As], E), nth0(X, E, E0), R0 < E0)
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).
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low_point(A, 0, Y) :-
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Y > 0,
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nth0(Y, A, [R0,R1|_]),
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R0 < R1,
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Y0 is Y - 1,
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Y1 is Y + 1,
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nth0(Y0, A, [T0|_]),
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R0 < T0,
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(
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length(A, Y1);
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(nth0(Y1, A, [E0|_]), R0 < E0)
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).
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low_point(A, X, Y) :-
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Y > 0,
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X > 0,
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nth0(Y, A, R),
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nth0(X, R, R0),
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X0 is X - 1,
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Y0 is Y - 1,
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X1 is X + 1,
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Y1 is Y + 1,
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nth0(X0, R, R1),
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R0 < R1,
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nth0(Y0, A, E),
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nth0(X, E, E0),
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R0 < E0,
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(
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(length(A, Y1), length(R, X1));
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(length(A, Y1), nth0(X1, R, R2), R0 < R2);
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(length(R, X1), nth0(Y1, A, T), nth0(X, T, T0), R0 < T0);
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(nth0(X1, R, R2), R0 < R2, nth0(Y1, A, T), nth0(X, T, T0), R0 < T0)
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).
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low_points([A|As], Ret) :-
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length([A|As], Y),
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length(A, X),
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X0 is X - 1,
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Y0 is Y - 1,
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low_points([A|As], X0, Y0, Ret).
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low_points(A, 0, 0, [[0, 0]]) :-
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low_point(A, 0, 0).
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low_points(A, 0, 0, []) :-
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\+ low_point(A, 0, 0).
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low_points(A, X, Y, [[X, Y]|Rs]) :-
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X > 0,
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low_point(A, X, Y),
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X0 is X - 1,
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low_points(A, X0, Y, Rs).
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low_points(A, X, Y, Rs) :-
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X > 0,
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\+ low_point(A, X, Y),
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X0 is X - 1,
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low_points(A, X0, Y, Rs).
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low_points([A|As], 0, Y, [[0, Y]|Rs]) :-
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Y > 0,
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length(A, Len),
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low_point([A|As], 0, Y),
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Y0 is Y - 1,
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X0 is Len - 1,
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low_points([A|As], X0, Y0, Rs).
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low_points([A|As], 0, Y, Rs) :-
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Y > 0,
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length(A, Len),
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\+ low_point([A|As], 0, Y),
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Y0 is Y - 1,
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X0 is Len - 1,
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low_points([A|As], X0, Y0, Rs).
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high_neighbor(A, [X1, Y1], [X0, Y0]) :-
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nth0(Y1, A, R1),
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nth0(Y0, A, R0),
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nth0(X1, R1, A1),
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A1 =\= 9,
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nth0(X0, R0, A0),
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A1 > A0.
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high_neighbors(A, X, Y, P) :-
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valid_paths(A, X, Y, W),
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setof(Q, (member(Q, W), high_neighbor(A, Q, [X, Y])), P).
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high_neighbors(A, X, Y, []) :-
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valid_paths(A, X, Y, W),
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\+ setof(Q, (member(Q, W), high_neighbor(A, Q, [X, Y])), _).
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points_high_neighbors(_, [], []).
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points_high_neighbors(A, [[X,Y]|Ps], N) :-
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points_high_neighbors(A, Ps, N1),
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high_neighbors(A, X, Y, N0),
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append(N0, N1, N2),
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sort(N2, N).
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points_high_neighbors_all(A, P, P) :-
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points_high_neighbors(A, P, []).
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points_high_neighbors_all(A, P, N) :-
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points_high_neighbors(A, P, N1),
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points_high_neighbors_all(A, N1, N2),
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append(P, N2, N3),
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sort(N3, N).
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in_bounds(W, H, X, Y) :-
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X >= 0, X < W,
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Y >= 0, Y < H.
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valid_paths([A|As], X, Y, P) :-
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length([A|As], H),
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length(A, W),
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valid_paths(W, H, X, Y, P).
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valid_paths(W, H, X, Y, [P|Ps]) :-
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X0 is X - 1, in_bounds(W, H, X0, Y), P = [X0, Y], valid_paths_1(W, H, X, Y, Ps).
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valid_paths(W, H, X, Y, Ps) :-
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X0 is X - 1,
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\+ in_bounds(W, H, X0, Y),
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valid_paths_1(W, H, X, Y, Ps).
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valid_paths_1(W, H, X, Y, [P|Ps]) :-
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X0 is X + 1, in_bounds(W, H, X0, Y), P = [X0, Y], valid_paths_2(W, H, X, Y, Ps).
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valid_paths_1(W, H, X, Y, Ps) :-
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X0 is X + 1, \+ in_bounds(W, H, X0, Y), valid_paths_2(W, H, X, Y, Ps).
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valid_paths_2(W, H, X, Y, [P|Ps]) :-
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Y0 is Y - 1, in_bounds(W, H, X, Y0), P = [X, Y0], valid_paths_3(W, H, X, Y, Ps).
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valid_paths_2(W, H, X, Y, Ps) :-
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Y0 is Y - 1, \+ in_bounds(W, H, X, Y0), valid_paths_3(W, H, X, Y, Ps).
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valid_paths_3(W, H, X, Y, [P]) :-
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Y0 is Y + 1, in_bounds(W, H, X, Y0), P = [X, Y0].
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valid_paths_3(W, H, X, Y, []) :-
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Y0 is Y + 1, \+ in_bounds(W, H, X, Y0).
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