# 76. Minimum Window Substring / Hard

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.

# Solution: Map + Sliding Window

–hmap[s[r]] >= 0

## 效能

### Complexity

• Time Complexity: O(M+N), which M and N are the length of string S and T
• Space Complexity: O(M+N)

### LeetCode Result

• Runtime: 4 ms
• Memory Usage: 7.6 MB