DIY: Minimum Window Substring

Problem statement

Suppose you are given two strings, say S and T. You have to find the smallest window substring of T. The smallest window substring is the shortest sequence of characters in S that includes all of the characters present in T with the same frequency.

Input

The input will be a string of characters.

# Example 1

S = "ABAACBBA" 
T = "ABC"

# Example 2

S = "ABAACBAB" 
T = "ABCC"

Output

The output will either contain a string of characters or an empty string.

# Example 1

"ACB"

# Example 2 

""

Coding exercise

You have to implement the minWindow function that takes two strings, S and T, and returns the minimum window substring of S, such that every character of T (including duplicates) is also present in the sequence. The sequence of the characters does not matter. If there is no such substring, you return an empty string.