DataEngPrep.tech
QuestionsBlogStore
Get PDF Bundle
Home/Questions/Python/Coding/Write a Python function to find the first non-repeating character in a string.

Write a Python function to find the first non-repeating character in a string.

Python/Codingeasy0.4 min readPremium
Frequency
Low
Asked at 2 companies
Category
179
questions in Python/Coding
Difficulty Split
127E|24M|28H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
AltimetrikInfosys
Interview Pro Tip

Red Flag: O(n²) solution with nested loops. Pro-Move: 'I use a single-pass with OrderedDict (char→count) and a set of seen-repeats; return first char not in repeats. Handles unicode and large inputs.'

Key Concepts Tested
python
Expert AnswerPremium
84 wordsInterview-ready
**Approach**: Two passes—first to count, second to find first with count 1. **Code**: `def first_non_repeating(s): counts = {}; [counts.update({c: counts.get(c, 0) + 1}) or None for c in s]; return next((c for c in s if counts[c] == 1), None)`. Simpler: `for c in s: counts[c] = counts.get(c,0)+1; return next((c for c in s if counts[c]==1), None)`. **Complexity**: O(n) time, O(k) space (k = distinct chars)....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like Altimetrik, Infosys. The answer also includes follow-up discussion points that interviewers commonly explore.

Continue Reading the Full Answer

Unlock the complete expert answer with code examples, trade-offs, and pro tips - plus 1,863+ more.

Create Free Account - Unlock 30 Answers
Get PDF Bundle - from $21

Or upgrade to Platform Pro - $39

Engineers who used these answers got offers at

AmazonDatabricksSnowflakeGoogleMeta

Related Python/Coding Questions

easyWhat are traits in Scala, and how are they different from classes?FreemediumWrite a Python function to check if a string is a palindrome.FreeeasyWhat is the difference between a list and a tuple in Python?FreeeasyExplain the difference between shallow copy and deep copy in Python.FreeeasyWrite a Python function to find the first non-repeating character in a string.Free

According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 2 companies. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

← Back to all questionsMore Python/Coding questions →