You are given two strings:

• log → a string representing system activity
• pattern → characters required to recover a password

Your task is to find the smallest continuous substring of log that contains all characters of pattern, including duplicate characters.

If no such substring exists, return an empty string "".

Function Requirement

Write a function that takes two strings log and pattern and returns the minimum window substring of log. If no valid window exists, return an empty string.

• Rules:

• Examples

• Constraints

• Hint