python实现LZ77
时间: 2023-07-07 13:38:41 浏览: 97
LZ77 是一种基于滑动窗口的无损数据压缩算法,下面是 Python 实现 LZ77 算法的代码示例:
```python
def lz77_compress(uncompressed):
window_size = 12
look_ahead_buffer_size = 5
compressed = []
pos = 0
while pos < len(uncompressed):
max_match_length = 0
max_match_distance = 0
for dist in range(1, window_size + 1):
start_pos = max(0, pos - dist)
match_length = 0
while pos + match_length < len(uncompressed) and uncompressed[start_pos + match_length] == uncompressed[pos + match_length] and match_length < look_ahead_buffer_size:
match_length += 1
if match_length > max_match_length:
max_match_length = match_length
max_match_distance = dist
if match_length == look_ahead_buffer_size:
break
if max_match_length > 0:
compressed.append((max_match_distance, max_match_length))
pos += max_match_length
else:
compressed.append((0, uncompressed[pos]))
pos += 1
return compressed
def lz77_decompress(compressed):
window_size = 12
decompressed = []
for item in compressed:
if item[0] == 0:
decompressed.append(item[1])
else:
start_pos = len(decompressed) - item[0]
for i in range(item[1]):
decompressed.append(decompressed[start_pos + i])
return ''.join(decompressed)
```
以上代码中,`lz77_compress` 函数实现了 LZ77 压缩算法,`lz77_decompress` 函数实现了 LZ77 解压缩算法。`window_size` 和 `look_ahead_buffer_size` 是两个参数,分别表示滑动窗口的大小和向前缓冲区的大小。`compressed` 列表存储压缩后的数据,每个元素是一个元组,包含匹配距离和匹配长度,如果匹配长度为 0,则表示当前位置是一个单独的字符。`lz77_decompress` 函数将压缩后的数据解压缩成原始数据。
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