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Contents
-module(trinary).
-export([to_decimal/1]).
-define(BASE, 3).
%%
%% trinary/ternary (base 3) to decimal (base 10)
%%
to_decimal(StringNumeric) ->
% numeric character list indexed by position
IndexedList = list_index(numeric_or(StringNumeric, "")),
% tokenize string into a list of numeric characters
Tokens = lists:foldl(fun accumulate/2, [], IndexedList),
% integer sum
round(lists:sum(Tokens)).
%%
%% if string is all numeric, return it; otherwise, return given default
%%
numeric_or(StringNumeric, Or) -> case re:run(StringNumeric, "^[0-9]+$") of
{match, _} -> StringNumeric;
nomatch -> Or
end.
%%
%% builds a numeric character list indexed by position (i.e. [{Num, Index}, ...])
%%
list_index(StringNumeric) ->
{Tuples, _} = lists:mapfoldr(fun index_accumulator/2, 0, StringNumeric), Tuples.
%%
%% Iterator to build tuples like `{Item, Index}` which correspond
%% to each item and its position in a list.
%%
%% element 1: numeric character
%% element 2: posision in the list (zero based) -- increase by one for each iteration
%%
index_accumulator(Item, Index) -> {{Item, Index}, Index + 1}.
%%
%% accumulate list values
%%
accumulate(T, Sum) ->
% destructure tuple into local vars
{Digit, Index} = T,
% cast binary into integer
Integer = binary_to_integer(<<Digit>>),
% append list to complete accumulation
Sum ++ [trinary(Integer, Index)].
%%
%% trinary algorithm (apply to each numeric character)
%%
trinary(Integer, Index) -> Integer * math:pow(?BASE, Index).
Version data entries
84 entries across 84 versions & 1 rubygems