class Solution {
public:
    int pivotIndex(vector<int>& nums) {
        int result = -1;
        int sum = 0 , left_sum=0;
        for(int it:nums) sum += it;
        for(int i=0 ; i<nums.size() ;i++)
        {
            if((sum-nums[i])%2 ==0  && (sum-nums[i])/2 == left_sum ) return i;
            else left_sum += nums[i];
        }
        return result;
    }
};