Given strings s1 and s2, return the minimum contiguous substring of s1 such that s2 is a subsequence of the substring. If there is no such window, return the empty string "". If there are multiple such windows of the same length, return the one with the smallest starting index.

• Two strings s1 and s2.

Input: s1 = "abcdebdde", s2 = "bde"
Output: "bcde"
Explanation: "bcde" is the minimum window that contains "bde" as a subsequence.