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lz77.py
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133 lines (111 loc) · 3.93 KB
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/**
* Copyright © https://github.com/microwind All rights reserved.
*
* @author: jarryli@gmail.com
* @version: 1.0
*/
import random
import base64
class Token:
"""LZ77压缩令牌类"""
def __init__(self, offset=0, length=0, character=None):
self.offset = offset
self.length = length
self.character = character
def __str__(self):
if self.length > 0:
return f"({self.offset},{self.length})"
else:
return f"({self.character})"
def lz77_compress(input_str):
"""
LZ77压缩算法
@param input_str: 输入字符串
@return: 压缩后的令牌列表
"""
print("LZ77压缩开始...")
tokens = []
window_size = 256
position = 0
while position < len(input_str):
max_length = min(window_size, position)
window = input_str[max(0, position - max_length):position]
best_length = 0
best_offset = 0
# 在窗口中搜索最长匹配
for i in range(len(window)):
match_length = 0
while (position + match_length < len(input_str) and
i + match_length < len(window) and
input_str[position + match_length] == window[i + match_length]):
match_length += 1
if match_length > best_length:
best_length = match_length
best_offset = len(window) - i
if best_length >= 3: # 最小匹配长度
next_char = input_str[position + best_length] if position + best_length < len(input_str) else None
tokens.append(Token(best_offset, best_length, next_char))
print(f"找到匹配: 偏移={best_offset}, 长度={best_length}")
position += best_length + 1
else:
tokens.append(Token(0, 0, input_str[position]))
print(f"字面量: {input_str[position]}")
position += 1
print(f"LZ77压缩完成，令牌数: {len(tokens)}")
return tokens
def lz77_decompress(tokens):
"""
LZ77解压算法
@param tokens: 压缩令牌列表
@return: 解压后的字符串
"""
print("LZ77解压开始...")
output = []
for i, token in enumerate(tokens):
print(f"处理令牌 {i}: {token}")
if token.length > 0:
start = len(output) - token.offset
for j in range(token.length):
output.append(output[start + j])
if token.character is not None:
output.append(token.character)
else:
output.append(token.character)
print(f"LZ77解压完成，长度: {len(output)}")
return ''.join(output)
def compression_ratio(original, compressed):
"""
计算压缩比
@param original: 原始字符串
@param compressed: 压缩令牌列表
@return: 压缩比
"""
original_size = len(original) * 8 # 假设每个字符8位
compressed_size = 0
for token in compressed:
compressed_size += 16 # 偏移和长度各8位
if token.length > 0:
compressed_size += 8 # 字符8位
return compressed_size / original_size
def main():
"""主函数，演示LZ77压缩和解压"""
input_str = "ABABABABABAABABABABA"
print("=== LZ77算法演示 ===")
print(f"原始文本: {input_str}")
print(f"原始长度: {len(input_str)}")
# 压缩
compressed = lz77_compress(input_str)
print(f"压缩结果: {compressed}")
# 计算压缩比
ratio = compression_ratio(input_str, compressed)
print(f"压缩比: {ratio:.2f}")
# 解压
decompressed = lz77_decompress(compressed)
print(f"解压结果: {decompressed}")
print(f"解压长度: {len(decompressed)}")
# 验证
is_valid = input_str == decompressed
print(f"验证结果: {'✓ 成功' if is_valid else '✗ 失败'}")
print("=== 演示结束 ===")
if __name__ == "__main__":
main()