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  1. f = ->a {a.group_by(&:upcase).select {|_,v| 1 < v.size}.values}
  2. p f.(readlines.map &:chomp)
Success #stdin #stdout 0s 28216KB
comments (?)
stdin
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aB.txt
Ab.txt
xx
cd
cD
CD
stdout
copy 
[["aB.txt", "Ab.txt"], ["cd", "cD", "CD"]]
https://ideone.com/faTKf5
language:
Ruby (ruby 2.5.5)
created:
6 years ago
visibility:
secret

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