Given a string s, return the first non-repeating character in it. If every character repeats, return null.
Examples:
Input: s = "aabbcddex"
Output: "c"
Input: s = "aabbcc"
Output: null
Input: s = "abcab"
Output: "c"
Input: s = "z"
Output: "z"
Apex Code Editor
Welcome to Lightning Challenge!
Create an Account
Sign up to track your progress, earn points, and compete with others. Your solutions will be saved automatically.
Create accountHow It Works
- • Write your solution in the code editor
- • Connect your Salesforce org to test
- • Submit to check if your solution passes
- • Use hints if you get stuck
Contest Alert
🏆 #CodeEveryDay Jan 2026
Contest runs January 1 - 31. Complete challenges to climb the leaderboard!
Points are calculated for challenges completed during the contest period.