Reverse a String Without Built-ins | Dataford Interview Questions

The Amazon Alexa test harness receives text payloads that may need to be reversed for validation. Write a function that returns the characters of a string in reverse order without using built-in reversal operations.

You may use character indexing, len, loops, and string concatenation. Do not use slicing such as s[::-1], reversed, list.reverse, join, or any library method that directly reverses or assembles the string.

Formal Specification

Implement reverse_string(s), where:

Input s is a Python string containing zero or more Unicode characters.
Output is a new string containing exactly the same characters in reverse order.
Spaces, punctuation, digits, repeated characters, and Unicode characters must be preserved exactly.
The function must not modify the input string.

Constraints

0 <= len(s) <= 10^4
s may contain any Unicode characters supported by Python strings
The input string must not be modified
Do not use slicing, reversed, list.reverse, join, or another direct reversal helper

Function Signature

def reverse_string(s):

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