[LeetCode238]Product of Array Except Self

题目：

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].

代码：

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