求哈夫曼编码的递归算法

以下是哈夫曼编码的递归算法演示：

class Node:
    def __init__(self, symbol, freq):
        self.symbol = symbol
        self.freq = freq
        self.left = None
        self.right = None

def huffman_coding(data):
    def build_huffman_tree(freq_dict):
        nodes = [Node(symbol, freq) for symbol, freq in freq_dict.items()]
        while len(nodes) > 1:
            nodes = sorted(nodes, key=lambda x: x.freq)
            left = nodes.pop(0)
            right = nodes.pop(0)
            parent = Node(None, left.freq + right.freq)
            parent.left = left
            parent.right = right
            nodes.append(parent)
        return nodes[0]

    def generate_huffman_code(node, current_code, huffman_codes):
        if node.symbol is not None:
            huffman_codes[node.symbol] = current_code
        else:
            generate_huffman_code(node.left, current_code + "0", huffman_codes)
            generate_huffman_code(node.right, current_code + "1", huffman_codes)

    freq_dict = {}
    for symbol in data:
        if symbol in freq_dict:
            freq_dict[symbol] += 1
        else:
            freq_dict[symbol] = 1

    root = build_huffman_tree(freq_dict)
    huffman_codes = {}
    generate_huffman_code(root, "", huffman_codes)
    return huffman_codes

data = "Huffman coding is a data compression algorithm."
huffman_table = huffman_coding(data)
print(huffman_table)