Sorting algorithms/Bubble sort: Difference between revisions

=={{header|Prolog}}==

It's surprisingly easy in Prolog while coding this sort, to accidentally create a sort that is similar, but not identical

to the bubble sort algorithm. Some of these are easier and shorter to code and work as well if not better. Having said that,

it's difficult to think of a reason to code the bubble sort these days except as an example of how not to sort your data.

<lang prolog>%___________________________________________________________________________

% Bubble sort

bubble(0, Res, Res, sorted).

bubble(Len, [A,B|T], Res, unsorted) :- A > B, !, bubble(Len,[B,A|T], Res, _).

bubble(Len, [A|T], [A|Ts], Ch) :- L is Len-1, bubble(L, T, Ts, Ch).

bubblesort(In, Out) :- length(In, Len), bubblesort(Len, In, Out).

bubblesort(0, In, In).

bubblesort(Len, In, Out) :-

bubble(Len, In, Bubbled, SortFlag), % bubble the list

(SortFlag=sorted -> !, Out=Bubbled; % list is already sorted

SegLen is Len - 1, !, % one fewer to process

writef('bubbled=%w\n', [Bubbled]), % show progress

bubblesort(SegLen, Bubbled, Out)).

test :- In = [8,9,1,3,4,2,6,5,4],

writef(' input=%w\n', [In]),

bubblesort(In, R),

writef('-> %w\n', [R]).</lang>