Re: array of strings - finding letter combinations

Hi Jan,

thank you so much for this. I went through the code and I think I
understand most of it. I am only having hard time understanding the
beginning:

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

What do these two lines define. I guess the second one is the regex,
what about the first one. And moreover, how are these two related?

I apologise if my questions are puzzling...

I plan to have the file with strings uploaded and then execute this code 
and probably print the results in a file as well.

regards,
seba


Jan E. wrote in post #1059205:
> 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?"
>     used_chars << unused
>   end
> end
>
> The actual processing of the user input has to be added, of course.

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