Given two strings `s`

and `t`

of lengths `m`

and `n`

respectively, 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 *`""`

*.*

The testcases will be generated such that the answer is **unique**.

A **substring** is a contiguous sequence of characters within the string.

**Example 1:**

**Input:** s = "ADOBECODEBANC", t = "ABC"
**Output:** "BANC"
**Explanation:** The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.

**Example 2:**

**Input:** s = "a", t = "a"
**Output:** "a"
**Explanation:** The entire string s is the minimum window.

**Example 3:**

**Input:** s = "a", t = "aa"
**Output:** ""
**Explanation:** Both 'a's from t must be included in the window.
Since the largest window of s only has one 'a', return empty string.

**Constraints:**

`m == s.length`

`n == t.length`

`1 <= m, n <= 10`^{5}

`s`

and `t`

consist of uppercase and lowercase English letters.

**Follow up:** Could you find an algorithm that runs in

`O(m + n)`

time?

Given two strings `s`

and `t`

of lengths `m`

and `n`

respectively, 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 *`""`

*.*

The testcases will be generated such that the answer is **unique**.

A **substring** is a contiguous sequence of characters within the string.

**Example 1:**

**Input:** s = "ADOBECODEBANC", t = "ABC"
**Output:** "BANC"
**Explanation:** The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.

**Example 2:**

**Input:** s = "a", t = "a"
**Output:** "a"
**Explanation:** The entire string s is the minimum window.

**Example 3:**

**Input:** s = "a", t = "aa"
**Output:** ""
**Explanation:** Both 'a's from t must be included in the window.
Since the largest window of s only has one 'a', return empty string.

**Constraints:**

`m == s.length`

`n == t.length`

`1 <= m, n <= 10`^{5}

`s`

and `t`

consist of uppercase and lowercase English letters.

**Follow up:** Could you find an algorithm that runs in

`O(m + n)`

time?