Reverse a String Using a Stack

Problem Reverse a given string using an explicit stack data structure, without using built-in reverse functions or two-pointer swapping.

Input / Output

• Input: a string s
• Output: the reversed string

Constraints

• 0 <= |s| <= 10^5
• Must use an explicit stack — the point is to demonstrate LIFO behaviour, not to find the fastest reversal
• O(n) time, O(n) extra space for the stack

Example

• Input: "hello" → Output: "olleh"
• Input: "ab" → Output: "ba"; empty string returns empty string