2、编写一个程序，构造哈夫曼树和哈夫曼编码，要求输出建立的哈夫曼树和相关的哈夫曼编码python和代码演示

好的，非常感谢您的提问。下面是使用 Python 编写的构造哈夫曼树和编码的示例代码。

from heapq import heappush, heappop, heapify
from collections import defaultdict

# 构造哈夫曼树
def huffman_tree(freq):
    heap = [[weight, [symbol, ""]] for symbol, weight in freq.items()]
    heapify(heap)
    while len(heap) > 1:
        lo = heappop(heap)
        hi = heappop(heap)
        for pair in lo[1:]:
            pair[1] = '0' + pair[1]
        for pair in hi[1:]:
            pair[1] = '1' + pair[1]
        heappush(heap, [lo[0] + hi[0]] + lo[1:] + hi[1:])
    return sorted(heappop(heap)[1:], key=lambda p: (len(p[-1]), p))

# 构造哈夫曼编码
def huffman_encoding(freq):
    code = {}
    for char, weight in freq.items():
        code[char] = ""
    tree = huffman_tree(freq)
    for pair in tree:
        code[pair[0]] = pair[1]
    return code

# 示例
if __name__ == "__main__":
    message = "hello world"
    freq = defaultdict(int)
    for symbol in message:
        freq[symbol] += 1
    code = huffman_encoding(freq)
    print("哈夫曼编码表:\n", code)

    encoded = "".join([code[symbol] for symbol in message])
    print("编码后的消息:\n", encoded)

    decoded = ""
    char_code = ""
    for bit in encoded:
        char_code += bit
        if char_code in code.values():
            decoded += list(code.keys())[list(code.values()).index(char_code)]
            char_code = ""
    print("解码后的消息:\n", decoded)

以上代码可以成功地构造哈夫曼树和哈夫曼编码，并输出相关信息。需要注意的是，示例中是使用默认字典 `defaultdict(int)` 来统计字符出现的频率。您可以将 `freq` 参数替换成任何可以表示字符频率的数据结构。