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.
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.This is the classic minimum window substring problem. The standard solution uses a sliding window with frequency counting: expand the right end until the window covers all required characters from t, then shrink from the left to minimize the current valid window. A hash map or array is used to track character counts efficiently, including duplicates. This approach is a strong interview pattern for two pointers, window maintenance, and frequency-based matching.
