238. Product of Array Except Self

该位置的积＝左边的积＊右边的积

class Solution {public:    vector<int> productExceptSelf(vector<int>& nums) {        int n=nums.size();        int i;        vector<int> output;        int P=1;                output.push_back(1);        for(i=1;i<n;i++)        {            output.push_back(output[i-1]*nums[i-1]);        }                for(i=n-2;i>=0;i--)        {            P=P*nums[i+1];            output[i]=output[i]*P;        }                return output;    }};