68 lines
1.7 KiB
Erlang
68 lines
1.7 KiB
Erlang
%% to compile: erlc day3A.erl
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%% to run: erl -noshell -s day5 solve
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%%
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-module(day17).
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-export ([solve/0, solve/1, solve/2]).
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-compile ([export_all]).
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solve() ->
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solve(['1']),
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solve(['2']),
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init:stop().
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solve(A) ->
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solve(A, read_input()).
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solve(['1'], D) ->
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io:format("The solution to ~p puzzle1 is: ~p~n", [?MODULE, solve(1, D)]);
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solve(1, D) ->
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solution1(D);
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solve(['2'], D) ->
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io:format("The solution to ~p puzzle2 is: ~p~n", [?MODULE, solve(2, D)]);
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solve(2, D) ->
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solution2(D).
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solution1({X,Y}) ->
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Xs = find_x(X),
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Ys = find_y(Y),
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{T, X1, Y1} = lists:max([{Key, X1, proplists:get_value(Key,Ys)} || {Key, X1} <- Xs, lists:keysearch(Key, 1, Ys) /= false]),
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y_max(T,Y1,0).
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solution2({X,Y}) ->
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Xs = find_x(X),
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Ys = find_y(Y),
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length(lists:usort([{X,Y} || {Ty, Y} <- Ys, {T,X} <- lists:filter(fun({T,X}) -> T == Ty end, Xs)])).
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read_input() ->
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{{124,174},{-123, -86}}.
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%% {{20,30},{-10, -5}}.
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find_x({Xmin, Xmax}) ->
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[ {T, Xstart} || Xstart <- lists:seq(0,400), T <- lists:seq(1,1000), x(Xstart, T) >= Xmin, x(Xstart, T) =< Xmax ].
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find_y({Ymin, Ymax}) ->
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[ {T, Ystart} || Ystart <- lists:seq(-400,400), T <- lists:seq(1,1000), y(Ystart, T) >= Ymin, y(Ystart, T) =< Ymax ].
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x(Xstart, T) ->
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Last =
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case (Xstart - T + 1) of
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L when L < 0 -> 0;
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L -> L
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end,
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(Xstart - Last + 1) * (Xstart + Last) div 2.
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y(Ystart, T) ->
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Last = (Ystart - T + 1),
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(Ystart - Last + 1) * (Ystart + Last) div 2.
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y_max(0, _, Ymax) -> Ymax;
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y_max(T, Y, Ymax) ->
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NewY = y(Y, T),
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NewMax =
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case NewY of
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M when M > Ymax -> M;
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_ -> Ymax
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end,
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y_max(T-1, Y, NewMax).
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