### Problem Statement

A String S is an interspersal of a set of Strings W, if W is a set of disjoint subsequences of S which cover S. Less formally, S can be formed from W by partitioning each member of W into substrings, then concatenating all the substrings, while maintaining the order of the substrings within each element of W. For example, if W contains the strings {"DESIGN", "ALGORITHM", "MARATHON"}, then one possible interspersal would be "ADELGMAORARISIGNTHMTHON", formed as shown below.

DE         SIGN

A  LG  O  RI    THM

MA RA         THON

-----------------------

Given a String[] W, return the lexicographically minimum interspersal of the Strings in W

### Definition

 Class: StringInterspersal Method: minimum Parameters: String[] Returns: String Method signature: String minimum(String[] W) (be sure your method is public)

### Notes

-The lexicographically minimum of two Strings is the one with the alphabetically earlier character at the first position at which they differ.
-The return String will contain no more than 1000 characters.

### Constraints

-W will contain between 1 and 20 elements, inclusive.
-Each element of W will contain between 1 and 50 uppercase letters ('A'-'Z'), inclusive.

### Examples

0)

 `{"DESIGN","ALGORITHM","MARATHON"}`
`Returns: "ADELGMAORARISIGNTHMTHON"`
 The example from the problem statement.
1)

 `{"TOMEK","PETR","ACRUSH","BURUNDUK","KRIJGERTJE"}`
`Returns: "ABCKPERIJGERRTJETOMEKTRURUNDUKUSH"`
2)

 `{"CCCA","CCCB","CCCD","CCCE"}`
`Returns: "CCCACCCBCCCCCCDE"`
3)

 `{"BKSDSOPTDD","DDODEVNKL","XX","PODEEE","LQQWRT"}`
`Returns: "BDDKLODEPODEEEQQSDSOPTDDVNKLWRTXX"`
4)

 `{"TOPCODER","BETFAIR","NSA","BT","LILLY"}`
`Returns: "BBELILLNSATFAIRTOPCODERTY"`
5)

 `{"QITHSQARQV","BYLHVGMLRY","LKMAQTJEAM","AQYICVNIKK","HKGZZFFEWC"}`
`Returns: "ABHKGLKMAQIQQTHSQARQTJEAMVYICVNIKKYLHVGMLRYZZFFEWC"`
6)

 `{"XHCYBTUQUW","EKBISADSSN","LOOISPOFAK","MIXBDHPJUQ","BNMNDHMOTC"}`
`Returns: "BEKBILMINMNDHMOOIOSADSPOFAKSSNTCXBDHPJUQXHCYBTUQUW"`

#### Problem url:

http://www.topcoder.com/stat?c=problem_statement&pm=8772

#### Problem stats url:

http://www.topcoder.com/tc?module=ProblemDetail&rd=13505&pm=8772

StevieT

#### Testers:

PabloGilberto , Olexiy , gawry , ivan_metelsky

#### Problem categories:

Greedy, String Manipulation