利用C++语言实现LZ78算法实现文本压缩,要求如下:输入需要英文文本的文件名,实现压缩,输出压缩后 的二进制文件文件;输入需要解压的二进制文件,实现解压 缩,输出原始的英文文本。
时间: 2023-06-26 08:03:59 浏览: 56
以下是C++代码实现LZ78算法的文本压缩和解压缩:
```cpp
#include <iostream>
#include <fstream>
#include <map>
#include <string>
#include <bitset>
using namespace std;
// 压缩函数
void compress(const string &inputFilename, const string &outputFilename) {
// 读取输入文件
ifstream inputFile(inputFilename, ios::binary);
if (!inputFile.is_open()) {
cerr << "Error: Failed to open input file.\n";
return;
}
string inputText((istreambuf_iterator<char>(inputFile)), istreambuf_iterator<char>());
inputFile.close();
// 构建字典
map<string, int> dictionary;
int nextCode = 0;
for (char c = 'a'; c <= 'z'; c++) {
string s(1, c);
dictionary[s] = ++nextCode;
}
// 压缩
ofstream outputFile(outputFilename, ios::binary);
int code = 0;
string prefix;
for (char c : inputText) {
string s = prefix + c;
if (dictionary.count(s)) {
prefix = s;
code = dictionary[s];
} else {
bitset<16> codeBits(code);
outputFile.write((char*)&codeBits, sizeof(bitset<16>));
outputFile.put(c);
dictionary[s] = ++nextCode;
prefix.clear();
code = 0;
}
}
if (!prefix.empty()) {
bitset<16> codeBits(code);
outputFile.write((char*)&codeBits, sizeof(bitset<16>));
}
outputFile.close();
cout << "Compression finished.\n";
}
// 解压缩函数
void decompress(const string &inputFilename, const string &outputFilename) {
// 读取输入文件
ifstream inputFile(inputFilename, ios::binary);
if (!inputFile.is_open()) {
cerr << "Error: Failed to open input file.\n";
return;
}
string inputText((istreambuf_iterator<char>(inputFile)), istreambuf_iterator<char>());
inputFile.close();
// 构建字典
map<int, string> dictionary;
int nextCode = 0;
for (char c = 'a'; c <= 'z'; c++) {
string s(1, c);
dictionary[++nextCode] = s;
}
// 解压缩
ofstream outputFile(outputFilename, ios::binary);
int code = 0;
string s;
for (int i = 0; i < inputText.size(); i += 3) {
bitset<16> codeBits(*(uint16_t*)(inputText.c_str() + i));
code = codeBits.to_ulong();
char c = inputText[i + 2];
if (dictionary.count(code)) {
s = dictionary[code];
s += c;
outputFile.write(s.c_str(), s.size());
dictionary[++nextCode] = s;
} else {
s = dictionary[code];
s += c;
outputFile.write(s.c_str(), s.size());
dictionary[++nextCode] = s;
}
}
outputFile.close();
cout << "Decompression finished.\n";
}
int main() {
// 压缩
string inputFilename = "input.txt";
string outputFilename = "compressed.bin";
compress(inputFilename, outputFilename);
// 解压缩
inputFilename = "compressed.bin";
outputFilename = "output.txt";
decompress(inputFilename, outputFilename);
return 0;
}
```
代码中使用`map`来作为字典,其中键为字符串,值为对应的编码。压缩时,从左到右扫描输入文本,维护一个前缀字符串`prefix`,并将当前字符加到其后面得到一个新字符串`s`。如果字典中已经存在`s`,那么将`s`作为新的前缀字符串,更新编码`code`为`s`对应的编码;否则,将`(code, c)`写入输出文件,将`s`加入字典并分配新的编码,清空前缀字符串和编码。这里使用了`bitset<16>`来存储编码,因为最多只有26个字母和一个空串,需要的编码数不会超过2^16。解压缩时,从左到右扫描压缩后的文件,读取每个2字节的编码和1个字符,如果字典中已经存在该编码,则将其对应的字符串`s`加上该字符输出,并将`(code, s+c)`加入字典;否则,将`(code, s+c)`输出,并将其加入字典。