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# 76. Minimum Window Substring

## Description

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?