Find the longest common starting substring in a set of strings [closed]

Answer 1

Yet another way to do it: use regex greed.

words = %w(interspecies interstelar interstate)
j = '='
str = ['', *words].join(j)
re = "[^#{j}]*"

str =~ /\A
    (?: #{j} ( #{re} ) #{re} )
    (?: #{j}    \1     #{re} )*
\z/x

p $1

And the one-liner, courtesy of mislav (50 characters):

p ARGV.join(' ').match(/^(\w*)\w*(?: \1\w*)*$/)[1]