lz77 采用python 语言实现,不使用python 库,并增加注释
时间: 2024-05-31 12:07:58 浏览: 9
# 首先定义一个函数,用于实现lz77压缩算法
def lz77_compress(input_string, look_ahead_buffer_size=15, search_buffer_size=4095):
"""
:param input_string: 待压缩的字符串
:param look_ahead_buffer_size: 向前看缓冲区大小
:param search_buffer_size: 搜索缓冲区大小
:return: 压缩后的字符串
"""
compressed_data = [] # 用于存放压缩后的数据
# 初始化搜索缓冲区和向前看缓冲区
search_buffer = ""
look_ahead_buffer = input_string[:look_ahead_buffer_size]
while len(look_ahead_buffer) > 0:
# 在搜索缓冲区中查找与向前看缓冲区相同的最长子串
index = -1
length = -1
for i in range(len(search_buffer)):
j = 0
while j < len(look_ahead_buffer) and i + j < len(search_buffer) and search_buffer[i + j] == look_ahead_buffer[j]:
j += 1
if j > length:
length = j
index = i
# 将最长匹配子串压缩成<offset, length>格式并存入压缩数据中
if length > 2:
offset = len(search_buffer) - index
compressed_data.append((offset, length))
look_ahead_buffer = look_ahead_buffer[length:]
else:
compressed_data.append((0, ord(look_ahead_buffer[0])))
look_ahead_buffer = look_ahead_buffer[1:]
# 更新搜索缓冲区和向前看缓冲区
search_buffer += input_string[:look_ahead_buffer_size]
input_string = input_string[look_ahead_buffer_size:]
search_buffer = search_buffer[-search_buffer_size:]
look_ahead_buffer = input_string[:look_ahead_buffer_size]
# 将压缩后的数据转换为字符串并返回
return ''.join([chr(x[0]) + chr(x[1]) if x[0] > 0 else chr(x[1]) for x in compressed_data])
# 定义一个函数,用于实现lz77解压缩算法
def lz77_decompress(input_string, look_ahead_buffer_size=15, search_buffer_size=4095):
"""
:param input_string: 待解压的字符串
:param look_ahead_buffer_size: 向前看缓冲区大小
:param search_buffer_size: 搜索缓冲区大小
:return: 解压后的字符串
"""
decompressed_data = [] # 用于存放解压后的数据
# 初始化搜索缓冲区和向前看缓冲区
search_buffer = ""
look_ahead_buffer = ""
for c in input_string:
# 将压缩数据还原成<offset, length>格式
if len(look_ahead_buffer) == look_ahead_buffer_size:
look_ahead_buffer = look_ahead_buffer[1:] + c
else:
look_ahead_buffer += c
if len(look_ahead_buffer) == 2:
offset = ord(look_ahead_buffer[0])
length = ord(look_ahead_buffer[1])
if offset == 0:
decompressed_data.append(length)
search_buffer += chr(length)
else:
start = len(search_buffer) - offset
for i in range(length):
decompressed_data.append(ord(search_buffer[start + i]))
search_buffer += chr(search_buffer[start + i])
search_buffer = search_buffer[-search_buffer_size:]
# 将解压后的数据转换为字符串并返回
return ''.join([chr(x) for x in decompressed_data])