Leetcode: Product of Array Except Self (60ms) analysis and solution

Problem:

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.)

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Analysis:

Using two round processing: forward and backward. See figure for detail:

//////////////////////////////////////////
//code 60ms
class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        vector<int> tmp(nums.size(), 1);
        int n=nums.size();
        //forward
        for(int i=0;i<n-1;i++){
            tmp[i+1]=tmp[i]*nums[i];
        }
        //backward
        int m=1;
        for (int j=n-1;j>-1;j--){
            tmp[j]=m*tmp[j];
            m=m*nums[j];
        }
        return tmp;
    }
};