How do I approach Coding & Algorithms interview questions?

Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

What difficulty level is this interview question?

This is a easy difficulty Coding & Algorithms question, commonly asked during Onsite rounds at Walmart Labs.

What role is this question designed for?

This question is commonly asked for Machine Learning Engineer candidates at Walmart Labs during technical interviews.

Find first non-repeating character | Walmart Labs Interview Question

Q: Find first non-repeating character

This question evaluates string manipulation, frequency-counting concepts, algorithmic complexity reasoning, and attention to edge-case handling in sequence data.

Walmart Labs

Dec 7, 2025, 12:00 AM

Machine Learning Engineer

Onsite

Coding & Algorithms

0

Loading...

Given a string s, return the first character that appears exactly once in the string (i.e., the leftmost non-repeating character).

If no such character exists, return an empty string (or a sentinel like "" ).

Examples

Input: "leetcode" → Output: "l"
Input: "aabb" → Output: ""

Constraints

1 ≤ len(s) ≤ 1e5
s contains standard ASCII letters/digits/punctuation (you may assume ASCII for counting).

Comments (0)

Sign in to leave a comment

Loading comments...

Browse More Questions

More Coding & Algorithms•More Walmart Labs•More Machine Learning Engineer•Walmart Labs Machine Learning Engineer•Walmart Labs Coding & Algorithms•Machine Learning Engineer Coding & Algorithms

Find first non-repeating character

Quick Overview