From: Xavier Noria <fxn@...>
Date: 2007-08-03T20:35:02+09:00
Subject: Re: Determining the common prefix for several strings

El Aug 3, 2007, a las 6:23 AM, Harry Kakueki escribi�:

> If I understood you correctly,  I think this will do it.
>
> r = ["itemz14","item004","item002","item002b","item 5","itemize this"]
>
> s = []
> a ,b = r.max.split(//), r.min.split(//)
> a.each_with_index{|x,y|s << y if x != b[y]}
> (0...s[0]).each {|x| print a[x]}

Good, so lexicographic order indeed helps. I would prefer to order  
the array only once though, and construct the prefix right ahead as a  
string so that the code reads more direct:

   prefix = ''
   min, max = items.sort.values_at(0, -1)
   min.split(//).each_with_index do |c, i|
     break if c != max[i, 1]
     prefix << c
   end
   puts prefix

My approach with splits removed and handling of the corner case where  
all items are equal is:

   prefix = items.first
   (0...items.first.length).each do |i|
     if items.map {|item| item[i, 1]}.uniq.length != 1
       prefix = prefix[0, i]
       break
     end
   end
   puts prefix

That solution does not order the array, but explicitly loops over all  
the columns in the prefix plus one via map, and uniqs them. The  
approach based on sort seems a bit better to me.

-- fxn