Smallest Window Problem Statement

Given two strings S and X containing random characters, the task is to find the smallest substring in S which contains all the characters present in X.

Input:

The first line contains an integer T representing the number of test cases. 
Each test case consists of two lines: 
1. A string S 
2. A string X

Output:

For each test case, print the smallest window in S which contains all the characters present in X, on a separate line.

Example:

Input:

S = "abdd"
X = "bd"

Output:

bd

Explanation:

The windows in S which contain all the characters in X are 'abdd', 'abd', 'bdd', 'bd'. The smallest substring in S which contains all the characters present in X is 'bd', which is the smallest in terms of length compared to other substrings.

Constraints:

• 1 ≤ T ≤ 10
• 1 ≤ |S|, |X| ≤ 105
• Time Limit: 1 sec

Note:

There is always a valid window in S which contains all the characters of X. In case of multiple answers, return the substring that occurs first.