Minimum Window Substring
Find the minimum window substring that contains all characters of another string.
Input: s = "a", t = "aa"
Output: "" (Empty String)
Explanation: The target requires two 'a's, but the source string only contains one, making it impossible to form a valid window.

Question

Find the minimum window substring that contains all characters of another string.

Input: s = "a", t = "aa"

Output: "" (Empty String)

Explanation: The target requires two 'a's, but the source string only contains one, making it impossible to form a valid window.