Leetcode 238. Product of Array Except Self

这里需要对累乘有比较充分的了解，那么做起来就很轻松。

class Solution {public:    vector<int> productExceptSelf(vector<int>& nums) {        int nums_len = nums.size();        vector<int> begin_vec(nums_len, 1);        int last_seq = 1;        int fst_seq = 1;        for(int i = 1; i < nums_len; i++)        {            fst_seq *= nums[i - 1];            begin_vec[i] *= fst_seq; // begin_vec[i - 1]*nums[i - 1];            begin_vec[nums_len - i] *= last_seq;             last_seq *= nums[nums_len - i];        }        begin_vec[0] = begin_vec[0] * last_seq;        return begin_vec;    }};