> First, we just shorten any symbols that are longer than our maximum code length — 11 — to that value. This means that our tree will no longer be a Huffman tree, so we need to do a fixup pass to redistribute the error we've introduced.

This can in fact be solved directly and optimally: https://en.wikipedia.org/wiki/Package-merge_algorithm ; https://en.wikipedia.org/wiki/Huffman_coding#Length-limited_...