// Minimum Window Substring — HARD

// Category: sliding-window

Given two strings `s` and `t` of lengths `m` and `n`, return the **minimum window substring** of `s` such that every character in `t` (including duplicates) is included in the window.

If no such substring exists, return an empty string.

Input format: `s|t`

Example: s = "ADOBECODEBANC", t = "ABC"

Output: "BANC"