class Solution:
    def pivotIndex(self, nums: List[int]) -> int:

        totalSum = sum(nums)
        runningSum = 0

        for i in range(len(nums)):
            leftSum = runningSum
            rightSum = totalSum - runningSum - nums[i]
            if leftSum == rightSum:
                return i
            runningSum += nums[i]

        return -1