add python code

public/py/ch4/huffman/huffman.py

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+"""
+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")