Smallest Window Problem Statement

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

Example:

Input:

S = "abdd", X = "bd"

Output:

"bd"

Explanation:

The substrings in S that contain all the characters in X are: "abdd", "abd", "bdd", "bd". Among these, "bd" is the smallest substring.

Constraints:

• 1 <= T <= 10
• 1 <= |S|, |X| <= 10^5
• Time Limit: 1 sec

Input:

The first line contains an integer T, the number of test cases.
Each test case consists of two lines:
- First line contains the string S.
- Second line contains the string X.

Output:

For each test case, print the smallest window in S containing all characters of X, on a separate line.

Note:

• There is always a valid window in S that contains all characters of X.
• If there are multiple smallest windows, return the one that appears first.