LeetCode Product of Array Except Self

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].
Solve it without division and in O(n).
For example, given [1,2,3,4], return [24,12,8,6].
Follow up:
Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        int len = nums.size();
        vector<int> res(len);
        
        int product = 1;
        for (int i=len - 1; i>=0; i--) {
            res[i] = product * nums[i];
            product = res[i];
        }
        product = 1;
        int end = len - 1;
        for (int i=0; i<end; i++) {
            res[i] = product * res[i+1];
            product *= nums[i];
        }
        res[end] = product;
        return res;
    }
};

比较简单的