请给出建立一个哈夫曼树的完整代码

以下是建立哈夫曼树的完整代码，包括构建哈夫曼树、编码和解码：

import heapq
from collections import defaultdict

class HuffmanCoding:
    def __init__(self, text):
        self.text = text
        self.freq = defaultdict(int)
        self.heap = []
        self.codes = {}
        self.reverse_mapping = {}

    # 构建哈夫曼树
    def make_heap(self):
        for char in self.text:
            self.freq[char] += 1
        for char in self.freq:
            heapq.heappush(self.heap, (self.freq[char], char))

    def merge_codes(self):
        while len(self.heap) > 1:
            freq1, char1 = heapq.heappop(self.heap)
            freq2, char2 = heapq.heappop(self.heap)

            merged_freq = freq1 + freq2
            merged_char = char1 + char2

            heapq.heappush(self.heap, (merged_freq, merged_char))

    def make_codes_helper(self, root, current_code):
        if root is None:
            return

        if len(root) == 1:
            char = root
            self.codes[char] = current_code
            self.reverse_mapping[current_code] = char
            return

        left, right = root
        self.make_codes_helper(left, current_code + "0")
        self.make_codes_helper(right, current_code + "1")

    def make_codes(self):
        root = heapq.heappop(self.heap)
        self.make_codes_helper(root, "")

    # 编码
    def get_encoded_text(self):
        encoded_text = ""
        for char in self.text:
            encoded_text += self.codes[char]
        return encoded_text

    # 解码
    def get_decoded_text(self, encoded_text):
        current_code = ""
        decoded_text = ""

        for bit in encoded_text:
            current_code += bit
            if current_code in self.reverse_mapping:
                char = self.reverse_mapping[current_code]
                decoded_text += char
                current_code = ""

        return decoded_text

    # 压缩
    def compress(self):
        self.make_heap()
        self.merge_codes()
        self.make_codes()
        encoded_text = self.get_encoded_text()
        return encoded_text

    # 解压缩
    def decompress(self, encoded_text):
        decoded_text = self.get_decoded_text(encoded_text)
        return decoded_text

使用示例：

text = "hello world"
h = HuffmanCoding(text)
encoded_text = h.compress()
decoded_text = h.decompress(encoded_text)

print(f"原文: {text}")
print(f"压缩后: {encoded_text}")
print(f"解压缩后: {decoded_text}")