Solution.java

class Solution {
    public int pivotIndex(int[] nums) {
        int totalSum = 0,
            leftSum = 0;
        
        for (int num : nums) totalSum += num;
        
        for (int i = 0; i < nums.length; i++) {
            if (leftSum == totalSum - nums[i] - leftSum) {
                return i;
            } else {
                leftSum += nums[i];
            }
        }
        
        return -1;
    }
}