Nth Non-Repeating Character | Dataford Interview Questions

A Zynga game event stream contains a sequence of characters representing compact player actions. Given a string s and a positive integer n, return the nth character that appears exactly once in the entire string, preserving the characters' original order.

Process the input string in a single left-to-right iteration. If fewer than n characters are non-repeating, return None.

Formal Specification

Input: s, a string, and n, a positive integer.
Output: The nth non-repeating character as a one-character string, or None if it does not exist.
Character comparisons are case-sensitive, so A and a are different characters.

Constraints

0 <= len(s) <= 10^5
1 <= n <= 10^5
Character comparisons are case-sensitive
The input string must be traversed only once

Function Signature

def find_nth_non_repeating(s, n):

Your question is Nth Non-Repeating Character. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem