Given two strings s and t, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".
Input: s = "ADOBECODEBANC", t = "ABC"
Output: "BANC"
Explanation: The minimum window substring "BANC" contains 'A', 'B', and 'C' from string t.
Input: s = "a", t = "a"
Output: "a"
Explanation: The entire string s is the minimum window.
Input: s = "a", t = "aa"
Output: ""
Explanation: Both 'a's from t must be included in the window, but s only contains one 'a', so return an empty string.
1 <= s.length, t.length <= 10^5s and t consist of uppercase and lowercase English letters.