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Erlang Fisher-Yates algorithm
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| shuffle_list(L) -> | |
| shuffle_list_sub(length(L), L). | |
| shuffle_list_sub(N, L) when N > 1 -> | |
| I = random:uniform(N), | |
| L2 = exchange_element(N, I, L), | |
| shuffle_list_sub(N - 1, L2); | |
| shuffle_list_sub(_N, L) -> | |
| L. | |
| exchange_element(N, N, L) -> L; | |
| exchange_element(N, I, L) -> | |
| A = lists:nth(I, L), | |
| {L1, [H | L2]} = lists:split(N - 1, L), | |
| LA = L1 ++ [A | L2], | |
| {L3, [_ | L4]} = lists:split(I - 1, LA), | |
| L3 ++ [H | L4]. | |
| %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | |
| knuth_yates([]) -> []; | |
| knuth_yates([_] = L) -> L; | |
| knuth_yates(L) -> shuffle_1(L, 1, erlang:length(L)). | |
| shuffle_1(L, Len, Len) -> L; | |
| shuffle_1(L, Cur, Len) -> | |
| S = Cur + erlang:round((Len - Cur) * rand:uniform()), | |
| L2 = swap_element(L, Cur, S), | |
| shuffle_1(L2, Cur + 1, Len). | |
| swap_element(L, N, N) -> L; | |
| swap_element(L, N1, N2) -> | |
| Z = lists:zip(lists:seq(1, length(L)), L), | |
| {value, E1} = lists:keysearch(N1, 1, Z), | |
| {value, E2} = lists:keysearch(N2, 1, Z), | |
| Z2 = lists:keyreplace(N1, 1, lists:keyreplace(N2, 1, Z, E1), E2), | |
| {_, Result} = lists:unzip(Z2), | |
| Result. |
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