Kevin's Stack Problem

Kevin requires assistance in reversing a string using the concept of a stack. Help Kevin by providing a solution that will reverse the string 'S' using a stack. The strings will only consist of English alphabets.

Example:

Input:

T = 1
S = "abcd"

Output:

"dcba"

Explanation:

The input string "abcd" is reversed to "dcba" using a stack.

Constraints:

• 1 <= T <= 10
• 1 <= |S| <= 10^4
• Time limit: 1 second