Most frequently asked interview question #4 with solution

Given a fixed length array arr of integers, duplicate each occurrence of zero, shifting the remaining elements to the right.
Note that elements beyond the length of the original array are not written.
Do the above modifications to the input array in place, do not return anything from your function.

Solution in C++:

    void duplicateZeros(vector<int>& arr) {
       
        int i = 0;
       
        int iter = 0;
        //Calculating the index before which array get terminated
            for(iter = 0; iter < arr.size(); ++i){
           
                //Case: If the digit is zero then increase by two
                if(arr.at(i) == 0){
                    iter = iter + 2;
                } else {
                    ++iter;
                }
            }
            --i;
            bool is_zero_only_once = false;
            if((iter > arr.size()) && (arr.at(i) == 0)){
                is_zero_only_once = true;
            }

            for(auto idx = arr.rbegin(); idx != arr.rend(); ++idx){
                if(arr.at(i) == 0){
                    *idx = 0;
                    if(is_zero_only_once == true){
                        is_zero_only_once = false;
                        --i;
                        continue;
                    }
                    ++idx;
                    if(idx == arr.rend()){
                        return;
                    }
                    *idx = 0;
                } else {
                    *idx = arr.at(i);
                }
                --i;
            }
    }