Given an array A of strings, find any smallest string that contains each string in A as a substring.
We may assume that no string in A is substring of another string in A.
Example 1:
Input: ["alex","loves","leetcode"] Output: "alexlovesleetcode" Explanation: All permutations of "alex","loves","leetcode" would also be accepted.
Example 2:
Input: ["catg","ctaagt","gcta","ttca","atgcatc"] Output: "gctaagttcatgcatc"
Note:
<li><code>1 <= A.length <= 12</code></li>
<li><code>1 <= A[i].length <= 20</code></li>