class Solution {
public:
    int pivotIndex(vector<int>& nums) {

        if(nums.size() == 0) return -1;

        vector<int> leftSum(nums.size(),0);

        for(auto i = 0; i < nums.size(); i++){
            leftSum[i] += nums[i];
        }

        for(auto i = 0; i < nums.size(); i++){
            if(2 * leftSum[i] - nums[i] == leftSum[nums.size() - 1]){
                return i;
            }
        }
        return -1;
    }
};