def _merge_sorted_nums_iter(sorted_nums1, sorted_nums2):
    """Helper method for merge_sort_iter().

    Merge two sorted lists by iteration.
    """
    # Apply two pointer method.
    i, j = 0, 0
    result = []

    for _ in range(len(sorted_nums1) + len(sorted_nums2)):
        if i < len(sorted_nums1) and j < len(sorted_nums2):
            if sorted_nums1[i] <= sorted_nums2[j]:
                result.append(sorted_nums1[i])
                i += 1
            else:
                result.append(sorted_nums2[j])
                j += 1      
        elif i < len(sorted_nums1) and j >= len(sorted_nums2):
            result.extend(sorted_nums1[i:])
            break
        elif i >= len(sorted_nums1) and j < len(sorted_nums2):
            result.extend(sorted_nums2[j:])
            break

    return result