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from pycompressor.priority_queue import MinPQ |
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from pycompressor.queue import Queue |
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from pycompressor.trie import TernarySearchTrie |
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class Node(object): |
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left = None |
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right = None |
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key = None |
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freq = 0 |
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def __init__(self, key=None, freq=None, left=None, right=None): |
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if key is not None: |
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self.key = key |
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if freq is not None: |
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self.freq = freq |
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if left is not None: |
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self.left = left |
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if right is not None: |
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self.right = right |
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def is_leaf(self): |
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return self.left is None and self.right is None |
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def char_at(text, i): |
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if len(text) - 1 < i: |
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return -1 |
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return ord(text[i]) |
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def write_char(char, bit_stream): |
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for i in range(8): |
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bit = char % 2 |
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bit_stream.enqueue(bit) |
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char = char // 2 |
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def read_char(bit_stream): |
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a = [0] * 8 |
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for i in range(8): |
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a[i] = bit_stream.dequeue() |
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char = 0 |
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for i in range(7, -1, -1): |
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char = char * 2 + a[i] |
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return char |
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class HuffmanCompressor(object): |
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def compress_to_binary(self, text): |
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trie = self.build_trie(text) |
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bit_stream = Queue() |
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code = {} |
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self.build_code(trie, '', code) |
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self.write_trie(trie, bit_stream) |
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self.write_text(code, text, bit_stream) |
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return bit_stream |
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def write_text(self, code, text, bit_stream): |
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for i in range(len(text)): |
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cc = code[char_at(text, i)] |
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for j in range(len(cc)): |
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if cc[j] == '0': |
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bit_stream.enqueue(0) |
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elif cc[j] == '1': |
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bit_stream.enqueue(1) |
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def build_code(self, x, prefix, code): |
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if x.is_leaf(): |
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code[x.key] = prefix |
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return |
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self.build_code(x.left, prefix + '0', code) |
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self.build_code(x.right, prefix + '1', code) |
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def build_trie(self, text): |
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search_trie = dict() |
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for i in range(len(text)): |
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c = char_at(text, i) |
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if c in search_trie: |
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search_trie[c].freq += 1 |
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else: |
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node = Node(key=c, freq=1) |
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search_trie[c] = node |
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pq = MinPQ(lambda x, y: x.freq - y.freq) |
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for node in search_trie.values(): |
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pq.enqueue(node) |
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while pq.size() > 1: |
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node1 = pq.del_min() |
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node2 = pq.del_min() |
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freq = node1.freq + node2.freq |
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node = Node(freq=freq, left=node1, right=node2) |
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pq.enqueue(node) |
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return pq.del_min() |
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def write_trie(self, x, bit_stream): |
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if x is None: |
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return |
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if x.is_leaf(): |
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bit_stream.enqueue(1) |
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write_char(x.key, bit_stream) |
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return |
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bit_stream.enqueue(0) |
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self.write_trie(x.left, bit_stream) |
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self.write_trie(x.right, bit_stream) |
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chen0040 /
pycompressor
