「円周上のCrossing」をErlangで(横へな14参考) ref: http://qiita.com/pazworld/items/a6a29d5d95200c0379b7

crosscircle.erl

-module(crosscircle).
-compile(export_all).

%% 解く
solve(Data) ->
  integer_to_list(solve([{X, 0} || X <- Data], 0)).

solve([], Total) ->
  Total;
solve([{FirstChar, _} | Rest], Total) ->
  WithDistance = line_to_distance(Rest),            % 線の本数→距離
  Distance = sum_distance(FirstChar, WithDistance), % 距離を合計
  LineAdded = add_line(FirstChar, Rest),            % 新たに線を引く
  solve(LineAdded, Total + Distance).               % 次の文字へ

%% 先頭から各文字までの距離(交差する線の数)を計算する
%% {文字, 線の数}のリストを受け取り{文字, 距離}のリストを返す
line_to_distance(L) ->
  F = fun({Char, Line}, {Distance, Ret}) ->
    {Distance + Line, [{Char, Distance} | Ret]} end,
  lists:reverse(element(2, lists:foldl(F, {0, []}, L))).

%% リストの先頭の文字から後続の同じ文字までの間に交差する線の数を返す
sum_distance(FirstChar, Rest) ->
  lists:sum([Distance || {Char, Distance} <- Rest, Char =:= FirstChar]).

%% リストの先頭の文字から後続の同じ文字へ線を引く
add_line(FirstChar, Rest) ->
  Same = fun(Char) -> % 同じ文字なら1、違う文字なら0を返す関数
    case Char of FirstChar -> 1; _ -> 0 end end,
  [{Char, Line + Same(Char)} || {Char, Line} <- Rest].

test(Data, Expected) ->
  Result = solve(Data),
  OkNg = case Result =:= Expected of true -> ok; false -> ng end,
  io:fwrite("~s: ~s -> ~s~n", [OkNg, Data, Result]).

tests() ->
  test("aabbca1bcb", "14"), %0
  test("111ZZZ", "0"), %1
  test("v", "0"), %2
  test("ww", "0"), %3
  test("xxx", "0"), %4
  test("yyyy", "1"), %5
  test("zzzzz", "5"), %6
  test("abcdef", "0"), %7
  test("abcaef", "0"), %8
  test("abbaee", "0"), %9
  test("abcacb", "2"), %10
  test("abcabc", "3"), %11
  test("abcdabcd", "6"), %12
  test("abcadeabcade", "23"), %13
  test("abcdeedcba", "0"), %14
  test("abcdeaedcba", "8"), %15
  test("abcdeaedcbad", "16"), %16
  test("QQQQXXXX", "2"), %17
  test("QwQQmQXmXXwX", "14"), %18
  test("111222333", "0"), %19
  test("aaAAaA", "4"), %20
  test("121232313", "12"), %21
  test("1ab1b", "1"), %22
  test("abcdefbadcfe", "12"), %23
  test("abxcdefbadcfex", "14"), %24
  test("dtnwtkt", "0"), %25
  test("mvubvpp", "0"), %26
  test("moggscd", "0"), %27
  test("kzkjzpkw", "2"), %28
  test("fbifybre", "1"), %29
  test("rrrfjryki", "1"), %30
  test("wrbbdwsdwtx", "2"), %31
  test("vvucugvxbvgx", "9"), %32
  test("ojkjzyasjwbfjj", "5"), %33
  test("ggffyuxnkyypifff", "5"), %34
  test("vcgtcqlwrepwvkkogl", "4"), %35
  test("xeqtmmgppwcjpcisogxbs", "4"), %36
  test("lukltpeucrqfvcupnpxwmoj", "6"), %37
  test("zpzswlkkoqwwndwpfdpkhtzgtn", "31"), %38
  test("bkfeflagfvluelududqjcvfyvytfw", "45"), %39
  test("rvqbhfmcjjqlpqzulzerxgyowiwrfkmhw", "26"), %40
  test("qyxvpdtoeexbqsethwjwmqszcxxjnsdoeaet", "144"), %41
  test("rjmsgmswhcolmpbhmpncziymydyalrcnevsrespj", "133"), %42
  test("oxetnyjzjbysnwktfwzndlejfndsqeetsnjvsicyjehd", "395"), %43
  test("wzvddnddzogywcqxbyvagbzmsmtcmrrlbnebmvhaemjouaqim", "219"), %44
  test("karhphxcxqgsyorhusbumbqzocuzvnwzwcpxgsksrviihxrgsrhji", "461"), %45
  test("oxgbononhqdxzmkysgijwvxljpaazmgkurkpffeuwywwuyxhyfkicgyzyc", "441"), %46
  test("sdgsrddwsrwqthhdvhrjhgtxwgurgyiygtktgtughtogzaqmcafkljgpniddsvb", "1077"), %47
  test("qemhecchkgzhxmdcsltwhpoyhkapckkkzosmklcvzkiiucrvzzznmhjfcdumuflavxik", "1711"), %48
  test("ffqmsirwpxrzfkbvmmfeptkbhnrvfcywthkwkbycmayhhkgvuyecbwwofwthlmzruphrcujwhr", "2440"). %49