def huffman(characters):
"""
Huffman codes compress data.
greedy algorithm, optimal substructure
If we assign a 3 bit codeword to each character, it takes 300k bits to encode a 100k character file
What if we use variable length codes?
prefix codes => no codeword is also a prefix of another codeword.
:param characters: list of characters
:return:
"""
n = len(characters)
queue = PriorityQueue(characters)
queue.build_min_heap()
for i in range(0, n-1):
new_node = Character()
new_node.left = queue.heap_extract_min()
new_node.right = queue.heap_extract_min()
new_node.freq = new_node.left.freq + new_node.right.freq
queue.min_heap_insert(new_node)
return queue.heap_extract_min()
