101 lines
2.6 KiB
Mathematica
101 lines
2.6 KiB
Mathematica
:- module day9.
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:- interface.
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:- import_module basics.
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:- pred run(part::in, lines::in, answer::out) is cc_multi.
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:- implementation.
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:- import_module int.
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:- import_module string.
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:- import_module list.
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:- import_module set_bbbtree.
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:- type set(T) == set_bbbtree(T).
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:- type coord ---> c(x :: int, y :: int).
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:- type rope == list(coord).
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:- type direction ---> up; down; left; right.
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:- pred to_direction(string, direction).
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:- mode to_direction(in, out) is semidet.
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:- mode to_direction(out, in) is det.
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to_direction("U", up).
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to_direction("D", down).
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to_direction("L", left).
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to_direction("R", right).
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:- pred orth(direction::in, direction::in) is semidet.
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orth(A, B) :-
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((A = up ; A = down), (B = left ; B = right));
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((A = left ; A = right), (B = up ; B = down)).
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:- pred line(string::in, list(direction)::out) is semidet.
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line(Str, replicate(N, D)) :-
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words(Str) = [DD, NN],
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to_direction(DD, D),
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to_int(NN, N).
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:- pred move_head(direction::out, coord::in, coord::out) is multi.
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move_head(up, c(X, Y), c(X, Y+1)).
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move_head(down, c(X, Y), c(X, Y-1)).
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move_head(left, c(X, Y), c(X-1, Y)).
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move_head(right, c(X, Y), c(X+1, Y)).
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:- pred ok(coord::in, coord::in) is semidet.
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ok(A, B) :- abs(A^x - B^x) =< 1, abs(A^y - B^y) =< 1.
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:- pred ok(rope::in) is semidet.
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ok([]). ok([_]).
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ok([A, B | Rest]) :- ok(A, B), ok([B | Rest]).
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:- pred same_rc(coord::in, coord::in) is semidet.
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same_rc(A, B) :- A^x = B^x ; A^y = B^y.
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:- pred move_tail1(coord::in, coord::in, coord::out) is nondet.
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move_tail1(H, !T) :- ok(H, !.T).
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move_tail1(H, !T) :-
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if same_rc(H, !.T) then
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move_head(_, !T),
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ok(H, !.T)
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else
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move_head(D1, !T),
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move_head(D2, !T),
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orth(D1, D2),
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ok(H, !.T).
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:- pred move_tail(coord::in, rope::in, rope::out) is nondet.
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move_tail(_, [], []).
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move_tail(H, [!.T | !.Ts], [!:T | !:Ts]) :-
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move_tail1(H, !T),
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move_tail(!.T, !Ts).
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:- pred move(direction::in, rope::in, rope::out) is nondet.
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move(_, [], []).
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move(D, [!.H | !.T], [!:H | !:T]) :-
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move_head(D, !H),
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move_tail(!.H, !T).
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:- type seen == set(coord).
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:- pred next(direction, rope, rope, seen, seen).
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:- mode next(in, in, out, in, out) is nondet.
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next(D, !Rope, !Seen) :-
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move(D, !Rope),
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last(!.Rope, Tail),
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insert(Tail, !Seen).
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:- pred run0(part::in, lines::in, int::out) is cc_nondet.
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run0(Part, Lines, Out) :-
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Start = replicate(part(Part, 2, 10), c(0, 0)),
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map(line, Lines, Dirs),
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foldl2(next, condense(Dirs), Start, _, init, End),
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count(End, Out).
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run(Part, Lines, int(Out)) :-
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disable_warning [no_solution_disjunct] (
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not run0(Part, Lines, Out) => die("bad input")
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).
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