Minimum Window Substring

Problem Given strings s and t, return the smallest substring (window) of s that contains every character of t including multiplicity. Return "" if no such window exists.

Input / Output

• Input: strings s and t.
• Output: the minimum window substring, or "".

Constraints

• 1 ≤ |s|, |t| ≤ 10^5.

Example

• s="ADOBECODEBANC", t="ABC" → "BANC"