Given two lists of strings, return a list containing only the elements that appear in both lists. The result should contain each common element only once and be sorted alphabetically. Handle null inputs by returning an empty list.
Examples:
Input: list1 = ['apple', 'banana', 'cherry'], list2 = ['banana', 'cherry', 'date']
Output: ['banana', 'cherry']
Explanation: Only banana and cherry appear in both lists, sorted alphabetically
Input: list1 = ['a', 'b', 'c'], list2 = ['d', 'e', 'f']
Output: []
Explanation: No common elements between the two lists
Input: list1 = null, list2 = ['a', 'b']
Output: []
Explanation: Null input returns empty list
Input: list1 = ['x', 'y'], list2 = null
Output: []
Explanation: Null input returns empty list
Apex Code Editor
Welcome to Lightning Challenge!
How 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 September 2026 (Sep 1–15)Sponsored by FLXBL
Contest runs September 1 - 15. Complete challenges to climb the leaderboard!
1st & 2nd: Salesforce certification exam voucher — see all prizes
Only the 15 daily challenges shown during this contest count toward points. Earlier dailies don't carry over.