Re: array of strings - finding letter combinations

Hi,

Sebastjan H. wrote in post #1059172:
>
> I am new to ruby and I want to learn by examples and here is one from my
> everyday work. I have an array of strings where each string contains a
> combination of an ampersand and a letter (&e). The trick is, this
> combination may only appear once in the whole array, so none of the
> other strings may contain the same combination.

You could start off by selecting the letter after "&" in a string. This 
can be done with a regex:

str = 'abc&exyz'
str[/(?<=&)[a-z]/]

Then you iterate over the array, collecting the duplicate strings and 
the used characters:

strings = ['&a', '&b', '&c', '&a']
used_chars = []
duplicates = []
strings.each_with_index do |str, i|
  char = str[/(?<=&)[a-z]/]
  duplicates << i if used_chars.include? char
  used_chars << char
end

And after this you iterate over the duplicate strings and suggest and 
unused character (or raise in error, if there are none left):

duplicates.each do |index|
  unused = ('a'..'z').find {|char| not used_chars.include? char}
  if unused.nil?
    raise 'all letters taken'
  else
    puts "combination #{strings[index][/&[a-z]/]} already taken.",
      "Use &#{unused} instead?"
  end
end

The actual processing of the user input has to added, of course.

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