简单的前缀和优化空间,先求出总和,然后用leftSum前缀和
class Solution {
public:
int pivotIndex(vector<int>& nums) {
int sum = 0, leftsum = 0;
for(auto num:nums) sum+=num;
for(int i=0;i<nums.size();i++){
if(leftsum==sum-leftsum-nums[i]) return i;
leftsum += nums[i];
}
return -1;
}
};