238. Product of Array Except Self

Problem Statement

• 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].

Approach

• There can be 2 cases
  1. There are zeroes in the array
     1. If there is more than 1 zero in the array the entire array product would be 0 (as there would always be one zero to be multiplied even if current element is zero)
     2. If there is one zero, all the products would be 0 except for the one where the current value is zero
  2. There are no zeroes in the array
     1. All products would be non-zero values
• Start by calculating the product of the entire array O(n) skipping the zeroes. then for each entry in the array calculate it's product value O(n)

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        long long product = 1;
        vector<int> result;
        int countZeroes = 0;
        for(auto a : nums)
            if(a != 0)
                product *= a;
            else
                countZeroes++;

        if(countZeroes > 1){
            vector<int> result(nums.size(), 0);
            return result;
        }

        for(auto a : nums){
            if(a != 0){
                if(countZeroes)
                    result.push_back(0);
                else
                    result.push_back(product/a);
            }else{
                result.push_back(product);
            }
        }
        return result;
    }
};