Creates regullar exp for anagram

anagram.rb

def anagram(input)
    lookaheadPart = ''
    matchingPart = '^'
    positiveLookaheadPrefix='(?='
    positiveLookaheadSuffix=')'

    letters = input.to_s.split('')
    inputCharacterFrequencyMap = letters.reduce(Hash.new(0)) { |a, b| a[b] += 1;  a  }
    inputCharacterFrequencyMap.each do |letter, freq|
      lookaheadPart += positiveLookaheadPrefix;
      freq.times{
        lookaheadPart += '.*'
        lookaheadPart += letter
        matchingPart += '.'
      }
      lookaheadPart += positiveLookaheadSuffix

    end
    matchingPart += '$'
    lookaheadPart + matchingPart

  end