First Non-Repeating Character

Problem

Given a string s, return the first character that appears exactly once while preserving the original order of characters. If no such character exists, return an empty string "". The input is a single string, and the output is a single character or an empty string.

Constraints

• 0 <= len(s) <= 10^5
• s contains printable characters
• Return the first unique character based on its original position