%   qsort
%
%   David H. D. Warren
%
%   quicksort a list of 50 integers

qsort(ShowResult) :-
	qsort([27,74,17,33,94,18,46,83,65,2,32,53,28,85,99,47,28,82,6,11,55,29,39,81,90,37,10,0,66,51,7,21,85,27,31,63,75,4,95,99,11,28,61,74,18,92,40,53,59,8], R, []),
	(   ShowResult = true ->
	    write(R), nl
	;   true).



qsort([], R, R).
qsort([X|L], R, R0) :-
	partition(L, X, L1, L2),
	qsort(L2, R1, R0),
	qsort(L1, R, [X|R1]).

partition([],_,[],[]).
partition([X|L],Y,[X|L1],L2) :-
	X =< Y, !,
	partition(L,Y,L1,L2).
partition([X|L],Y,L1,[X|L2]) :-
	partition(L,Y,L1,L2).


% benchmark interface

benchmark(ShowResult) :-
	qsort(ShowResult).

:- include(common).