def huffman(C):
n = len(C)
Q = PriorityQueue(C, MinHeap)
for i in range(n - 1):
x = Q.extract_min()
y = Q.extract_min()
z = Node(x.key() + y.key())
z.left = x
z.right = y
Q.insert(z)
return Q.extract_min()
