Doesn't seem that complicated if you're not too concerned about ultimate performance:
def common_substring(data)
data.inject { |m, s| s[0,(0..m.length).find { |i| m[i] != s[i] }.to_i] }
end
One of the useful features of inject is the ability to pre-seed with the first element of the array being interated over. This avoids the nil memo check.
puts common_substring(%w[ interspecies interstelar interstate ]).inspect
# => "inters"
puts common_substring(%w[ feet feel feeble ]).inspect
# => "fee"
puts common_substring(%w[ fine firkin fail ]).inspect
# => "f"
puts common_substring(%w[ alpha bravo charlie ]).inspect
# => ""
puts common_substring(%w[ fork ]).inspect
# => "fork"
puts common_substring(%w[ fork forks ]).inspect
# => "fork"
Update: If golf is the game here, then 67 characters:
def f(d)d.inject{|m,s|s[0,(0..m.size).find{|i|m[i]!=s[i]}.to_i]}end
