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Ingy döt Net 2013-04-11 01:07:29 -07:00
parent b83f433714
commit 68f8f3e56b
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Task/Sorting-algorithms-Merge-sort/Mercury/sorting-algorithms-merge-sort.mercury Normal file
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:- func merge_sort(list(T)) = list(T).
merge_sort(U) = S :- merge_sort(U, S).
:- pred merge_sort(list(T)::in, list(T)::out) is det.
merge_sort(U, S) :- merge_sort(list.length(U), U, S).
:- pred merge_sort(int::in, list(T)::in, list(T)::out) is det.
merge_sort(L, U, S) :-
( L > 1 ->
H = L // 2,
( split(H, U, F, B) ->
merge_sort(H, F, SF),
merge_sort(L - H, B, SB),
merge(SF, SB, S)
; throw(split_error) )
; S = U ).
:- pred split(int::in, list(T)::in, list(T)::out, list(T)::out) is semidet.
split(N, L, S, E) :-
( N = 0 -> S = [], E = L
; N > 0, L = [H | L1], S = [H | S1],
split(N - 1, L1, S1, E) ).
:- pred merge(list(T)::in, list(T)::in, list(T)::out) is det.
merge([], [], []).
merge([X|Xs], [], [X|Xs]).
merge([], [Y|Ys], [Y|Ys]).
merge([X|Xs], [Y|Ys], M) :-
( compare(>, A, B) ->
merge([X|Xs], Ys, M0),
C = [Y|C0]
; merge(Xs, [Y|Ys], C0),
C = [X|C0] ).