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

:- ensure_loaded(harness).

benchmark(Data, Out) :-
	qsort(Data, Out, []).

data([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]).

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).