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

        cumsum = 0
        for num in nums:
            cumsum += num

        left_sum = 0
        for i in range(len(nums)):
            right_sum = cumsum - left_sum - nums[i]
            if left_sum == right_sum:
                return i
            left_sum = left_sum + nums[i]

        return -1