(哈夫曼压缩)将01字符串转换为二进制文件的方法
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// 你没说什么语言！如果需要其它的话，我再翻译一下！
// 没什么效率，但是满足需求了
import java.io.*;
public class Z {
public static void main(String[] args) throws Exception {
//System.out.println(decode(encode("00001000")));
//System.out.println(decode(encode("11111000")));
writeHuffman("011");
System.out.println(read()Huffman());
}
// 每次传进去的字符串都是8个字符长度，刚好能够表示一个byte
public static byte encode(String s) {
int a = 0;
for ( int i = 0; i < 8; i++) {
char ch = s.charAt(i);
a = a << 1;
if (ch == '1') {
a = a | 0x1;
}
}
return (byte)a;
}
// 上一步的逆操作
public static String decode(byte b) {
StringBuilder sb = new StringBuilder();
for ( int i = 0; i < 8; i++) {
sb.append((b & (0x1 << (7 - i))) > 0 ? '1' : '0');
}
return sb.toString();
}
// 再写一下文件操作
// 假设你已经得到了通过huffman树编码的字符串，那么就这样写写入文件
public static void writeHuffman(String s) throws Exception {
// 因为huffman编码字符串不总是8个字符的倍数，那么我们不足8时补0，并记录我们到底补了几个。
// 我们把补位数放在文件的第一个字节
int z = 8 - s.length() % 8;
if (z == 8) {
z = 0;
}
byte[] buffer = new byte[1024];
buffer[0] = (byte)z;
int pos = 1, nBytes = (int)(Math.ceil(s.length()/((double)8)));
File f = new File("test.huffman");
FileOutputStream os = new FileOutputStream(f);
for ( int i = 0; i < nBytes; i++) {
String ss;
if (s.length() >= (i + 1) * 8) {
ss = s.substring(i * 8, (i + 1) * 8);
} else {
ss = s.substring(i * 8);
while (ss.length() < 8) {
ss = new StringBuilder(ss).append('0').toString();
}
}
buffer[pos] = encode(ss);
pos++;
if (pos == 1024) {
os.write(buffer);
pos = 0;
}
}
if (pos > 0) {
os.write(buffer, 0, pos);
}
os.close();
}
// 我们把压缩过的文本放在test.huffman里面
public static String readHuffman() throws Exception {
File f = new File("test.huffman");
FileInputStream fs = new FileInputStream(f);
byte[] buffer = new byte[1024];
int len = 0;
StringBuilder sb = new StringBuilder();
byte z = (byte)fs.read();
while ((len = fs.read(buffer)) != -1) {
for ( int i = 0; i < len; i++) {
sb.append(decode(buffer[i]));
}
}
fs.close();
return sb.substring(0, sb.length() - z);
}
}
c++ 版本
#include "stdafx.h"#include <stdio.h>
#include <iostream>
#include <string>
#include <cmath>
using namespace std;
unsigned char encode(const char *s) {
int a = 0;
for ( int i = 0; i < 8; i++) {
if (s[i] == '1') {
a = a | (0x1 << (7 - i));
}
}
return (unsigned char)a;
}
void decode(unsigned char a, char *buf) {
for ( int i = 0; i < 8; i++) {
buf[i] = (((a >> (7 - i)) & 0x1) != 0) ? '1' : '0';
}
}
void writeHuffman(const string& s) {
unsigned char z = 8 - s.length() % 8;
if (z == 8) {
z = 0;
}
unsigned char buffer[1024];
buffer[0] = z;
int pos = 1, nBytes = (int)(ceil(s.length() / ((double)8)));
const char* ps = s.c_str();
FILE *fp = fopen("test.huffman", "wb");
char extended[8];
for ( int i = 0; i < nBytes; i++) {
const char *p;
if (s.length() >= (i + 1) * 8) {
p = ps + i * 8;
}
else {
char *pp = extended;
for ( int j = i * 8; j < s.length(); j++) {
*pp = s[j];
pp++;
}
for (int j = 0; j < z; j++) {
*pp = '0';
pp++;
}
p = extended;
}
buffer[pos] = encode(p);
pos++;
if (pos == 1024) {
fwrite(buffer, sizeof(unsigned char), 1024, fp);
pos = 0;
}
}
if (pos > 0) {
fwrite(buffer, sizeof(unsigned char), pos, fp);
}
fclose(fp);
}
string& readHuffman() {
FILE *fp = fopen("test.huffman", "rb");
fseek(fp, 0L, SEEK_END);
size_t fileSize = ftell(fp);
rewind(fp);
unsigned char buffer[1024];
fread(buffer, sizeof(unsigned char), 1, fp);
unsigned char z = buffer[0];
size_t stringSize = (fileSize - 1) * 8;
char *ptr = new char[stringSize + 1];
char *optr = ptr;
size_t len;
while ((len = fread(buffer, sizeof(unsigned char), 1024, fp)) != 0) {
for ( int i = 0; i < len; i++) {
decode(buffer[i], ptr);
ptr = ptr + 8;
}
}
fclose(fp);
ptr = ptr - z;
*ptr = '\0';
string* str = new string(optr);
delete []optr;
return *str;
}
int main(void)
{
writeHuffman("00010");
cout << readHuffman() << endl;
getchar();
return 0;
}
