* most num_used_symbols - 1 intermediate nodes when creating a Huffman
* code. This is because if there were at least num_used_symbols nodes,
* the code would be suboptimal because there would be at least one
* most num_used_symbols - 1 intermediate nodes when creating a Huffman
* code. This is because if there were at least num_used_symbols nodes,
* the code would be suboptimal because there would be at least one