Product of Array Except Self

Problem Statement - link #

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

You must write an algorithm that runs in O(n) time and without using the division operation.

Examples #

Example 1:

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

Example 2:

Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]

Constraints #

• 2 <= nums.length <= 10^5
• -30 <= nums[i] <= 30
• The product of any prefix or suffix of nums is guaranteed to fit in a *32-bit integer.

Follow up: #

Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)

Solution #

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        vector<int> lp(nums.size(),1);
        vector<int> rp(nums.size(),1);
        for(int i = 1; i < nums.size(); i++)
            lp[i] = lp[i-1]*nums[i-1];
        for(int i = nums.size()-2; i >= 0 ; i--)
            rp[i] = rp[i+1]*nums[i+1];
        for(int i = 0; i < nums.size(); i++)
            nums[i] = lp[i]*rp[i];
        
        return nums;
        
    }
};