%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2009. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(queue).
%% Creation, inspection and conversion
-export([new/0,is_queue/1,is_empty/1,len/1,to_list/1,from_list/1,member/2]).
%% Original style API
-export([in/2,in_r/2,out/1,out_r/1]).
%% Less garbage style API
-export([get/1,get_r/1,peek/1,peek_r/1,drop/1,drop_r/1]).
%% Higher level API
-export([reverse/1,join/2,split/2,filter/2]).
%% Okasaki API from klacke
-export([cons/2,head/1,tail/1,
snoc/2,last/1,daeh/1,init/1,liat/1,lait/1]).
%%--------------------------------------------------------------------------
%% Efficient implementation of double ended fifo queues
%%
%% Queue representation
%%
%% {RearList,FrontList}
%%
%% The first element in the queue is at the head of the FrontList
%% The last element in the queue is at the head of the RearList,
%% that is; the RearList is reversed.
%%
%% A declaration equivalent to the following is currently hard-coded
%% in erl_types.erl
%%
%% -opaque queue() :: {list(), list()}.
%% Creation, inspection and conversion
%% O(1)
-spec new() -> queue().
new() -> {[],[]}. %{RearList,FrontList}
%% O(1)
-spec is_queue(term()) -> boolean().
is_queue({R,F}) when is_list(R), is_list(F) ->
true;
is_queue(_) ->
false.
%% O(1)
-spec is_empty(queue()) -> boolean().
is_empty({[],[]}) ->
true;
is_empty({In,Out}) when is_list(In), is_list(Out) ->
false;
is_empty(Q) ->
erlang:error(badarg, [Q]).
%% O(len(Q))
-spec len(queue()) -> non_neg_integer().
len({R,F}) when is_list(R), is_list(F) ->
length(R)+length(F);
len(Q) ->
erlang:error(badarg, [Q]).
%% O(len(Q))
-spec to_list(queue()) -> list().
to_list({In,Out}) when is_list(In), is_list(Out) ->
Out++lists:reverse(In, []);
to_list(Q) ->
erlang:error(badarg, [Q]).
%% Create queue from list
%%
%% O(length(L))
-spec from_list(list()) -> queue().
from_list(L) when is_list(L) ->
f2r(L);
from_list(L) ->
erlang:error(badarg, [L]).
%% Return true or false depending on if element is in queue
%%
%% O(length(Q)) worst case
-spec member(term(), queue()) -> boolean().
member(X, {R,F}) when is_list(R), is_list(F) ->
lists:member(X, R) orelse lists:member(X, F);
member(X, Q) ->
erlang:error(badarg, [X,Q]).
%%--------------------------------------------------------------------------
%% Original style API
%% Append to tail/rear
%% Put at least one element in each list, if it is cheap
%%
%% O(1)
-spec in(term(), queue()) -> queue().
in(X, {[_]=In,[]}) ->
{[X], In};
in(X, {In,Out}) when is_list(In), is_list(Out) ->
{[X|In],Out};
in(X, Q) ->
erlang:error(badarg, [X,Q]).
%% Prepend to head/front
%% Put at least one element in each list, if it is cheap
%%
%% O(1)
-spec in_r(term(), queue()) -> queue().
in_r(X, {[],[_]=F}) ->
{F,[X]};
in_r(X, {R,F}) when is_list(R), is_list(F) ->
{R,[X|F]};
in_r(X, Q) ->
erlang:error(badarg, [X,Q]).
%% Take from head/front
%%
%% O(1) amortized, O(len(Q)) worst case
-spec out(queue()) -> {'empty' | {'value',term()}, queue()}.
out({[],[]}=Q) ->
{empty,Q};
out({[V],[]}) ->
{{value,V},{[],[]}};
out({[Y|In],[]}) ->
[V|Out] = lists:reverse(In, []),
{{value,V},{[Y],Out}};
out({In,[V]}) when is_list(In) ->
{{value,V},r2f(In)};
out({In,[V|Out]}) when is_list(In) ->
{{value,V},{In,Out}};
out(Q) ->
erlang:error(badarg, [Q]).
%% Take from tail/rear
%%
%% O(1) amortized, O(len(Q)) worst case
-spec out_r(queue()) -> {'empty' | {'value',term()}, queue()}.
out_r({[],[]}=Q) ->
{empty,Q};
out_r({[],[V]}) ->
{{value,V},{[],[]}};
out_r({[],[Y|Out]}) ->
[V|In] = lists:reverse(Out, []),
{{value,V},{In,[Y]}};
out_r({[V],Out}) when is_list(Out) ->
{{value,V},f2r(Out)};
out_r({[V|In],Out}) when is_list(Out) ->
{{value,V},{In,Out}};
out_r(Q) ->
erlang:error(badarg, [Q]).
%%--------------------------------------------------------------------------
%% Less garbage style API.
%% Return the first element in the queue
%%
%% O(1) since the queue is supposed to be well formed
-spec get(queue()) -> term().
get({[],[]}=Q) ->
erlang:error(empty, [Q]);
get({R,F}) when is_list(R), is_list(F) ->
get(R, F);
get(Q) ->
erlang:error(badarg, [Q]).
-spec get(list(), list()) -> term().
get(R, [H|_]) when is_list(R) ->
H;
get([H], []) ->
H;
get([_|R], []) -> % malformed queue -> O(len(Q))
lists:last(R).
%% Return the last element in the queue
%%
%% O(1) since the queue is supposed to be well formed
-spec get_r(queue()) -> term().
get_r({[],[]}=Q) ->
erlang:error(empty, [Q]);
get_r({[H|_],F}) when is_list(F) ->
H;
get_r({[],[H]}) ->
H;
get_r({[],[_|F]}) -> % malformed queue -> O(len(Q))
lists:last(F);
get_r(Q) ->
erlang:error(badarg, [Q]).
%% Return the first element in the queue
%%
%% O(1) since the queue is supposed to be well formed
-spec peek(queue()) -> 'empty' | {'value',term()}.
peek({[],[]}) ->
empty;
peek({R,[H|_]}) when is_list(R) ->
{value,H};
peek({[H],[]}) ->
{value,H};
peek({[_|R],[]}) -> % malformed queue -> O(len(Q))
{value,lists:last(R)};
peek(Q) ->
erlang:error(badarg, [Q]).
%% Return the last element in the queue
%%
%% O(1) since the queue is supposed to be well formed
-spec peek_r(queue()) -> 'empty' | {'value',term()}.
peek_r({[],[]}) ->
empty;
peek_r({[H|_],F}) when is_list(F) ->
{value,H};
peek_r({[],[H]}) ->
{value,H};
peek_r({[],[_|R]}) -> % malformed queue -> O(len(Q))
{value,lists:last(R)};
peek_r(Q) ->
erlang:error(badarg, [Q]).
%% Remove the first element and return resulting queue
%%
%% O(1) amortized
-spec drop(queue()) -> queue().
drop({[],[]}=Q) ->
erlang:error(empty, [Q]);
drop({[_],[]}) ->
{[],[]};
drop({[Y|R],[]}) ->
[_|F] = lists:reverse(R, []),
{[Y],F};
drop({R, [_]}) when is_list(R) ->
r2f(R);
drop({R, [_|F]}) when is_list(R) ->
{R,F};
drop(Q) ->
erlang:error(badarg, [Q]).
%% Remove the last element and return resulting queue
%%
%% O(1) amortized
-spec drop_r(queue()) -> queue().
drop_r({[],[]}=Q) ->
erlang:error(empty, [Q]);
drop_r({[],[_]}) ->
{[],[]};
drop_r({[],[Y|F]}) ->
[_|R] = lists:reverse(F, []),
{R,[Y]};
drop_r({[_], F}) when is_list(F) ->
f2r(F);
drop_r({[_|R], F}) when is_list(F) ->
{R,F};
drop_r(Q) ->
erlang:error(badarg, [Q]).
%%--------------------------------------------------------------------------
%% Higher level API
%% Return reversed queue
%%
%% O(1)
-spec reverse(queue()) -> queue().
reverse({R,F}) when is_list(R), is_list(F) ->
{F,R};
reverse(Q) ->
erlang:error(badarg, [Q]).
%% Join two queues
%%
%% Q2 empty: O(1)
%% else: O(len(Q1))
-spec join(queue(), queue()) -> queue().
join({R,F}=Q, {[],[]}) when is_list(R), is_list(F) ->
Q;
join({[],[]}, {R,F}=Q) when is_list(R), is_list(F) ->
Q;
join({R1,F1}, {R2,F2}) when is_list(R1), is_list(F1), is_list(R2), is_list(F2) ->
{R2,F1++lists:reverse(R1,F2)};
join(Q1, Q2) ->
erlang:error(badarg, [Q1,Q2]).
%% Split a queue in two
%%
%% N = 0..len(Q)
%% O(max(N, len(Q)))
-spec split(non_neg_integer(), queue()) -> {queue(),queue()}.
split(0, {R,F}=Q) when is_list(R), is_list(F) ->
{{[],[]},Q};
split(N, {R,F}=Q) when is_integer(N), N >= 1, is_list(R), is_list(F) ->
Lf = erlang:length(F),
if N < Lf -> % Lf >= 2
[X|F1] = F,
split_f1_to_r2(N-1, R, F1, [], [X]);
N > Lf ->
Lr = length(R),
M = Lr - (N-Lf),
if M < 0 ->
erlang:error(badarg, [N,Q]);
M > 0 ->
[X|R1] = R,
split_r1_to_f2(M-1, R1, F, [X], []);
true -> % M == 0
{Q,{[],[]}}
end;
true -> % N == Lf
{f2r(F),r2f(R)}
end;
split(N, Q) ->
erlang:error(badarg, [N,Q]).
%% Move N elements from F1 to R2
split_f1_to_r2(0, R1, F1, R2, F2) ->
{{R2,F2},{R1,F1}};
split_f1_to_r2(N, R1, [X|F1], R2, F2) ->
split_f1_to_r2(N-1, R1, F1, [X|R2], F2).
%% Move N elements from R1 to F2
split_r1_to_f2(0, R1, F1, R2, F2) ->
{{R1,F1},{R2,F2}};
split_r1_to_f2(N, [X|R1], F1, R2, F2) ->
split_r1_to_f2(N-1, R1, F1, R2, [X|F2]).
%% filter, or rather filtermap with insert, traverses in queue order
%%
%% Fun(_) -> List: O(length(List) * len(Q))
%% else: O(len(Q)
-spec filter(fun((term()) -> boolean() | list()), queue()) -> queue().
filter(Fun, {R0,F0}) when is_function(Fun, 1), is_list(R0), is_list(F0) ->
F = filter_f(Fun, F0),
R = filter_r(Fun, R0),
if R =:= [] ->
f2r(F);
F =:= [] ->
r2f(R);
true ->
{R,F}
end;
filter(Fun, Q) ->
erlang:error(badarg, [Fun,Q]).
%% Call Fun in head to tail order
filter_f(_, []) ->
[];
filter_f(Fun, [X|F]) ->
case Fun(X) of
true ->
[X|filter_f(Fun, F)];
false ->
filter_f(Fun, F);
L when is_list(L) ->
L++filter_f(Fun, F)
end.
%% Call Fun in reverse order, i.e tail to head
%% and reverse list result from fun to match queue order
filter_r(_, []) ->
[];
filter_r(Fun, [X|R0]) ->
R = filter_r(Fun, R0),
case Fun(X) of
true ->
[X|R];
false ->
R;
L when is_list(L) ->
lists:reverse(L, R)
end.
%%--------------------------------------------------------------------------
%% Okasaki API inspired by an Erlang user contribution "deque.erl"
%% by Claes Wikstrom <[email protected]> 1999.
%%
%% This implementation does not use the internal data format from Klacke's
%% doubly ended queues that was "shamelessly stolen" from
%% "Purely Functional Data structures" by Chris Okasaki, since the data
%% format of this module must remain the same in case some application
%% has saved a queue in external format or sends it to an old node.
%%
%% This implementation tries to do the best of the situation and should
%% be almost as efficient as Okasaki's queues, except for len/1 that
%% is O(n) in this implementation instead of O(1).
%%
%% The new representation in this module again adds length field and
%% fixes this, but it is not yet default.
%%
%% The implementation keeps at least one element in both the forward
%% and the reversed lists to ensure that i.e head/1 or last/1 will
%% not have to reverse a list to find the element.
%%
%% To be compatible with the old version of this module, as much data as
%% possible is moved to the receiving side using lists:reverse/2 when data
%% is needed, except for two elements (when possible). These two elements
%% are kept to prevent alternating tail/1 and init/1 operations from
%% moving data back and forth between the sides.
%%
%% An alternative would be to balance for equal list length when one side
%% is exhausted. Although this could be better for a general double
%% ended queue, it would more han double the amortized cost for
%% the normal case (one way queue).
%% Cons to head
%%
-spec cons(term(), queue()) -> queue().
cons(X, Q) ->
in_r(X, Q).
%% Return head element
%%
%% Return the first element in the queue
%%
%% O(1) since the queue is supposed to be well formed
-spec head(queue()) -> term().
head({[],[]}=Q) ->
erlang:error(empty, [Q]);
head({R,F}) when is_list(R), is_list(F) ->
get(R, F);
head(Q) ->
erlang:error(badarg, [Q]).
%% Remove head element and return resulting queue
%%
-spec tail(queue()) -> queue().
tail(Q) ->
drop(Q).
%% Functions operating on the other end of the queue
%% Cons to tail
%%
-spec snoc(queue(), term()) -> queue().
snoc(Q, X) ->
in(X, Q).
%% Return last element
-spec daeh(queue()) -> term().
daeh(Q) -> get_r(Q).
-spec last(queue()) -> term().
last(Q) -> get_r(Q).
%% Remove last element and return resulting queue
-spec liat(queue()) -> queue().
liat(Q) -> drop_r(Q).
-spec lait(queue()) -> queue().
lait(Q) -> drop_r(Q). %% Oops, mis-spelled 'tail' reversed. Forget this one.
-spec init(queue()) -> queue().
init(Q) -> drop_r(Q).
%%--------------------------------------------------------------------------
%% Internal workers
-compile({inline, [{r2f,1},{f2r,1}]}).
%% Move all but two from R to F, if there are at least three
r2f([]) ->
{[],[]};
r2f([_]=R) ->
{[],R};
r2f([X,Y]) ->
{[X],[Y]};
r2f([X,Y|R]) ->
{[X,Y],lists:reverse(R, [])}.
%% Move all but two from F to R, if there are enough
f2r([]) ->
{[],[]};
f2r([_]=F) ->
{F,[]};
f2r([X,Y]) ->
{[Y],[X]};
f2r([X,Y|F]) ->
{lists:reverse(F, []),[X,Y]}.
