Merge One Sorted Array Into Another Solution 1

    static ArrayList<Integer> merge_one_into_another(ArrayList<Integer> arr1, ArrayList<Integer> arr2) {

        // moving all numbers in arr2 to the second half
        for(int i = 0; i < arr1.size(); i++)
        {
            Collections.swap(arr2, i, arr1.size() + i);
        }

        int i = 0;
        int j = arr1.size();
        int idx = 0;

        // sorting from left side
        while(i < arr1.size() && j < arr2.size())  {
            if(arr1.get(i) <= arr2.get(j)) {
                arr2.set(idx, arr1.get(i));
                arr1.set(i, 0);
                i++;
                idx++;
            } else {
                arr2.set(idx, arr2.get(j));
                arr2.set(j, 0);
                j++;
                idx++;
            }
        }

        // put remaining elements in arr1 to arr2
        while(i < arr1.size())
        {
            arr2.set(idx, arr1.get(i));
            arr1.set(i, 0);
            i++;
            idx++;
        }

        return arr2;
    }