238. Product of Array Except Self

• Difficulty: Medium

• Topics: Array

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Problem:

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]

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.)

Solutions:

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        int n = nums.size();
        vector<int> ret (n, 1);

        for (int i = n - 2; i >= 0; --i) {
            ret[i] *= ret[i + 1] * nums[i + 1];
        }

        int product = 1;
        for (int i = 0; i < n; ++i) {
            ret[i] *= product;
            product *= nums[i];
        }

        return ret;
    }
};