Compare

PROBLEM STATEMENT
A string k is a subsequence of a string x if the letters of k appear in order
in x.  i.e., "abc" is a subsequence of "azzzzbzzzzc". "abc" is also a
subsequence of "abc" and of "abcabc".  However, "abc" is not a subsequence of
"acb", since the letters to not appear in order.

DEFINITION
Class name: Compare
Method name: shortest
Parameters: String, String
Returns: String

Method signature (make sure it is declared public):
String shortest(String tofind, String base);

Given two Strings, you must determine what the shortest substring of base that
contains tofind as a subsequence. If multiple substrings of the same shortest
length exist, return the one that occurs first in base.

If the tofind subsequence does not exist in base, return the empty string "".

TopCoder will enforce the following restrictions:
* tofind will be between 1 and 6 characters, inclusive.
* base will be between 1 and 12 characters, inclusive.
* tofind and base will contain only lowercase letters (a-z).

EXAMPLES
tofind = "abc"
base = "aabbc"
There are two substrings containing "abc" as a subsequence: "aabbc", and "abbc"
Since "abbc" is shorter, method returns "abbc".

tofind = "ab"
base = "efaefbeecc"
method returns "aefb".

tofind = "abc"
base = "abeecacabffc"
method returns "abeec". Note that "abffc" is also valid and of the same length,
but "abeec" occurs first, and thus is the correct answer.

tofind = "aid"
base = "abidhelloaid"
method returns "aid".