Given a list of integers, find the equilibrium index where the sum of elements to the left equals the sum of elements to the right. The element at the equilibrium index is not included in either sum. Return -1 if no equilibrium index exists. Return -1 for null or empty input.
Examples:
Input: nums = (1, 3, 5, 2, 2)
Output: 2
Explanation: Left sum = 1+3 = 4, Right sum = 2+2 = 4, equilibrium at index 2
Input: nums = (0, 1, -1)
Output: 0
Explanation: Left sum = 0 (nothing to the left), Right sum = 1+(-1) = 0
Input: nums = (1, 2, 3)
Output: -1
Explanation: No index where left sum equals right sum
Input: nums = (5)
Output: 0
Explanation: Single element always has equilibrium at index 0
Input: nums = null
Output: -1
Explanation: Null input returns -1
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 June 2026
Contest runs June 1 - 30. Complete challenges to climb the leaderboard!
Only the 30 daily challenges shown during this contest count toward points. Earlier dailies don't carry over.