「回文の発掘」をErlangで(横へな15参考)

「回文の発掘」をErlangでやってみました。他の実装は 第15回オフラインリアルタイムどう書くの参考問題 から辿れます。

subpalin.erl

-module(subpalin).
-compile(export_all).

%% 解く
solve(Data) -> integer_to_list(palinnum(Data)).

%% 回文の最大長を返す
palinnum([]) -> 0;
palinnum(L) -> lists:max([palinnum2(S) || S <- tailcombi(L)]).

palinnum2([]) -> 0;
palinnum2([H | T]) ->
  F = fun % 先頭と同じ文字を探し、その間に含まれる回文の最大長を返す関数
    ([H2 | T2]) when H2 =:= H -> palinnum(lists:reverse(T2)) + 1;
    (_) -> 0
  end,
  lists:max([0 | [F(X) || X <- tailcombi(lists:reverse(T))]]) + 1.

%% "abc" -> ["abc", "bc", "c"]
tailcombi(L) -> tailcombi(L, []).

tailcombi([], Acc) -> lists:reverse(Acc);
tailcombi(L = [_ | T], Acc) -> tailcombi(T, [L | Acc]).

%% テスト
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("I_believe_you_can_solve", "9"), %0
  test("a", "1"), %1
  test("aa", "2"), %2
  test("aaa", "3"), %3
  test("ab", "1"), %4
  test("aabb", "2"), %5
  test("ABBA", "4"), %6
  test("Abba", "2"), %7
  test("1234567890", "1"), %8
  test("1234567890987654321", "19"), %9
  test("abcdcba", "7"), %10
  test("0a1b2c3d4c5b6a7", "7"), %11
  test("abcdcba0123210", "7"), %12
  test("abcdcba_123210", "7"), %13
  test("_bcdcba0123210", "7"), %14
  test("abcddcba0123210", "8"), %15
  test("abcdcba01233210", "8"), %16
  test("a0bc1dc2ba3210a", "9"), %17
  test("a0bc1ddc2ba3210", "8"), %18
  test("3a0bc1ddc2ba3210", "10"), %19
  test("11oooo1111o1oo1o111ooooooooooo", "20"), %20
  test("11o1111o1111oo11ooo11111ooo1oo", "20"), %21
  test("111111oo11o111ooo1o1ooo11ooo1o", "21"), %22
  test("11o1o1o11oo11o11oo111o1o1o11oo", "27"), %23
  test("oo111o1o11o1oo1ooo11o1o11o1o1o", "27"), %24
  test("1o1oo11111o1o1oo1o1o1111oo1o1o", "28"), %25
  test("QQooooQooooQQyQoyQQQyyyyQQoyoy", "15"), %26
  test("oQoooQooooQyoyQoyoyyyQQyQQQQoQ", "16"), %27
  test("yyyyyooyQyyyoyyQyyooyQoQoQQoQy", "17"), %28
  test("yyQoyQoyyQyQQoyooooyyQQyQyooQy", "24"), %29
  test("oQQooQoQyQQoyoQQoQyQyQyQoQoooo", "24"), %30
  test("oQQyQQyyQyQQoooyQQyyyQQQyyQQoy", "25"), %31
  test("WAk9iHI4jVDlStyudwTNqE138kwan2", "3"), %32
  test("c43fIu1Mlz0K9hEVOgGcUdbeB5ksa7", "3"), %33
  test("CAbYcW5VqHjzFdIkH_61PM0TsyRuie", "3"), %34
  test("jInQnUvSayrJTsQWujovbbqW0STvoj", "10"), %35
  test("iZDrvpUKgtj3FrZsZ4CLjrEgUdZzQG", "11"), %36
  test("ROgYUOu6er_DA7nB6UGquO1GUHC62R", "11"), %37
  test("Oh_be_a_fine_girl_kiss_me", "9"), %38
  test("8086_6502_6809_Z80", "11"), %39
  test("xcode_visualstudio_eclipse", "11"), %40
  test("word_excel_powerpoint_outlook", "9"), %41
  test("abcdefghijklmnopqrstuvwxyz0123", "1"). %42