'''
Description: 
Autor: Au3C2
Date: 2021-01-28 10:25:31
LastEditors: Au3C2
LastEditTime: 2021-01-28 10:25:57
'''
class Solution:
    def pivotIndex(self, nums: List[int]) -> int:
        n = len(nums)
        if not nums:
            return -1
        leftSum = 0
        rightSum = sum(nums)-nums[0]
        for i in range(n-1):
            if leftSum == rightSum:
                return i
            leftSum += nums[i]
            rightSum -= nums[i+1]
        if leftSum == rightSum:
            return i + 1
        return -1

# 数组，简单，每日一题。下标要仔细
# https://leetcode-cn.com/problems/find-pivot-index/