Problem Statement

Create a routine that, given a set of strings representing directory paths and a single character directory separator, will return a string representing that part of the directory tree that is common to all the directories. Test your routine using the forward slash '/' character as the directory separator and the following three strings as input paths: Note: The resultant path should be the valid directory '/home/user1/tmp' and not the longest common string '/home/user1/tmp/cove'. If your language has a routine that performs this function (even if it does not have a changeable separator character), then mention it as part of the task.

Let's start with the solution:

(use '[clojure.string :only [join,split]]) 

(defn common-prefix [sep paths]
  (let [parts-per-path (map #(split % (re-pattern sep)) paths)
        parts-per-position (apply map vector parts-per-path)]
    (join sep
      (for [parts parts-per-position :while (apply = parts)]
        (first parts)))))

(println
  (common-prefix "/"
    ["/home/user1/tmp/coverage/test"
     "/home/user1/tmp/covert/operator"
     "/home/user1/tmp/coven/members"]))