Count the number of unique words in a sentence in a case insensitive manner. Words are sequences of letters or digits. Punctuation and separators are ignored. Return 0 for an empty string. Return null for null input.
Examples:
Input: sentence = "Hello, hello world"
Output: 2
Explanation: Unique words are hello and world
Input: sentence = "One two TWO three"
Output: 3
Explanation: Unique words are one, two, three
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 May 2026
Contest runs May 1 - 31. Complete challenges to climb the leaderboard!
Only the 31 daily challenges shown during this contest count toward points. Earlier dailies don't carry over.