Given a string s, return the first character that appears exactly once when scanning from left to right. If no such character exists, return an empty string "". Write a Python function that solves this efficiently and be prepared to analyze its time complexity.
Example 1:
Input: s = "leetcode"
Output: "l"
Explanation: 'l' is the first character whose frequency is 1.
Example 2:
Input: s = "aabb"
Output: ""
Explanation: Every character appears more than once.
Example 3:
Input: s = "swiss"
Output: "w"
Explanation: 'w' is the first non-repeating character from left to right.
0 <= len(s) <= 10^5s consists of printable characters"" if no non-repeating character existsGiven a string s, return the first character that appears exactly once when scanning from left to right. If no such character exists, return an empty string "". Write a Python function that solves this efficiently and be prepared to analyze its time complexity.
Example 1:
Input: s = "leetcode"
Output: "l"
Explanation: 'l' is the first character whose frequency is 1.
Example 2:
Input: s = "aabb"
Output: ""
Explanation: Every character appears more than once.
Example 3:
Input: s = "swiss"
Output: "w"
Explanation: 'w' is the first non-repeating character from left to right.
0 <= len(s) <= 10^5s consists of printable characters"" if no non-repeating character exists