Initialize possible_dups to 0 and length_ to the length of the array minus 1.
Iterate through the array, counting the number of possible duplicates (possible_dups) and adjusting the length (length_) to account for the space needed for duplicating zeros.
Start from the last element in the array, move each element to its new position, and duplicate zeros when encountered, taking care to handle the edge case for the zero at the boundary.
Continue this process until all elements have been moved and duplicated as necessary.