wk2 238. Product of Array Except Self

Difficulty: Medium

Given an array of n integers where n > 1, nums, return an arrayoutput such that output[i] is equal to the product of all the elements ofnums 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 s = nums.size(), i = 0;        vector<int> <code>output</code>(s, 1);        for (i = 1; i < s; ++i)            <code>output</code>[i] = <code>output</code>[i-1] * nums[i-1];        int k = nums[s-1];        for (i = s - 2; i >=0; --i)        {            <code>output</code>[i] *= k;            k *= nums[i];        }        return <code>output</code>;    }};

思路是先计算output[i]左边所有数的乘积，再计算output[i]右边所有数的乘积，用两个for循环来完成计算。