"""
Huffman 编码 — 贪心算法
构建最优前缀码实现数据压缩
"""
import heapq
from collections import Counter

class HuffmanNode:
    def __init__(self, char, freq):
        self.char = char
        self.freq = freq
        self.left = None
        self.right = None

    def __lt__(self, other):
        return self.freq < other.freq

def build_huffman_tree(text):
    """构建 Huffman 树"""
    freq = Counter(text)
    heap = [HuffmanNode(char, f) for char, f in freq.items()]
    heapq.heapify(heap)

    while len(heap) > 1:
        left = heapq.heappop(heap)
        right = heapq.heappop(heap)
        merged = HuffmanNode(None, left.freq + right.freq)
        merged.left = left
        merged.right = right
        heapq.heappush(heap, merged)

    return heap[0] if heap else None

def generate_codes(node, prefix="", code_map=None):
    """从 Huffman 树生成编码"""
    if code_map is None:
        code_map = {}

    if node is None:
        return code_map

    if node.char is not None:
        code_map[node.char] = prefix or "0"
    else:
        generate_codes(node.left, prefix + "0", code_map)
        generate_codes(node.right, prefix + "1", code_map)

    return code_map

if __name__ == "__main__":
    text = "ABRACADABRA"
    print(f"原文: {text}")

    root = build_huffman_tree(text)
    codes = generate_codes(root)

    print("\nHuffman 编码:")
    for char, code in sorted(codes.items()):
        print(f"  '{char}': {code}")

    encoded = "".join(codes[c] for c in text)
    print(f"\n编码结果: {encoded}")
    print(f"原始大小: {len(text) * 8} bits")
    print(f"压缩大小: {len(encoded)} bits")