238. Product of Array Except Self（图解）

238. Product of Array Except Self

Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Example:

Input:  [1,2,3,4]
Output: [24,12,8,6]

Constraint: It’s guaranteed that the product of the elements of any prefix or suffix of the array (including the whole array) fits in a 32 bit integer.

Note: Please solve it without division and in O(n).

Follow up:
Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)

Solution

C++

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

Explanation