You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
100 lines
2.7 KiB
Java
100 lines
2.7 KiB
Java
import java.io.FileInputStream;
|
|
import java.util.*;
|
|
|
|
public class Lzw {
|
|
static final char END = (char) 0xFFFF;
|
|
|
|
public static int[] lzwEncoding(String s) {
|
|
List<Integer> result = new ArrayList<>();
|
|
Map<String, Integer> dict = new HashMap<>();
|
|
int cnt = 0;
|
|
for (int i = 0; i < 256; i++)
|
|
dict.put(String.valueOf((char) i), cnt++);
|
|
dict.put(String.valueOf(END), cnt++);
|
|
String cur = "";
|
|
for (char ch : s.toCharArray()) {
|
|
cur += ch;
|
|
if (!dict.containsKey(cur)) {
|
|
Integer e = dict.get(cur.substring(0, cur.length() - 1));
|
|
result.add(e);
|
|
dict.put(cur, cnt++);
|
|
cur = String.valueOf(ch);
|
|
}
|
|
}
|
|
result.add(dict.get(cur));
|
|
result.add(dict.get(String.valueOf(END)));
|
|
int[] res = new int[result.size()];
|
|
for (int i = 0; i < res.length; i++)
|
|
res[i] = result.get(i);
|
|
System.out.printf("Dict items: %,d\n", dict.size());
|
|
// System.out.printf("Dict size: %,d\n", SizingAgent.deepSizeOf(dict));
|
|
return res;
|
|
}
|
|
|
|
public static String lzwDecoding(int[] s) {
|
|
StringBuilder sb = new StringBuilder();
|
|
Map<Integer, String> dict = new HashMap<>();
|
|
int cnt = 0;
|
|
for (int i = 0; i < 256; i++)
|
|
dict.put(cnt++, String.valueOf((char) i));
|
|
dict.put(cnt++, String.valueOf(END));
|
|
|
|
String cur = dict.get(s[0]);
|
|
sb.append(cur);
|
|
char a = cur.charAt(0);
|
|
|
|
for (int i = 1; i < s.length; i++) {
|
|
int code = s[i];
|
|
if (code < cnt) {
|
|
String str = dict.get(code);
|
|
a = str.charAt(0);
|
|
if (a == END)
|
|
break;
|
|
dict.put(cnt++, cur + a);
|
|
sb.append(str);
|
|
cur = str;
|
|
} else {
|
|
cur += a;
|
|
dict.put(cnt++, cur);
|
|
sb.append(cur);
|
|
}
|
|
}
|
|
|
|
return sb.toString();
|
|
}
|
|
|
|
// Usage example
|
|
public static void main(String[] args) throws Exception {
|
|
FileInputStream fs = new FileInputStream("src/Lzw.java");
|
|
byte[] data = new byte[1_000_000];
|
|
int len = fs.read(data, 0, data.length);
|
|
data = Arrays.copyOf(data, len);
|
|
char[] buffer = new char[len];
|
|
for (int i = 0; i < len; i++)
|
|
buffer[i] = (char) (Byte.toUnsignedInt(data[i]));
|
|
String s = new String(buffer, 0, len);
|
|
int[] encoded = lzwEncoding(s);
|
|
String s2 = lzwDecoding(encoded);
|
|
byte[] data2 = new byte[len];
|
|
for (int i = 0; i < len; i++)
|
|
data2[i] = (byte) s2.charAt(i);
|
|
System.out.println(Arrays.equals(data, data2));
|
|
Locale.setDefault(Locale.US);
|
|
System.out.printf("%d -> %.0f\n", s.length(), optimalCompressedLength(encoded));
|
|
}
|
|
|
|
static double optimalCompressedLength(int[] a) {
|
|
int max = 0;
|
|
for (int x : a)
|
|
max = Math.max(max, x);
|
|
int[] freq = new int[max + 1];
|
|
for (int x : a)
|
|
++freq[x];
|
|
double optimalLength = 0;
|
|
for (int f : freq)
|
|
if (f > 0)
|
|
optimalLength += f * Math.log((double) a.length / f) / Math.log(2) / 8;
|
|
return optimalLength;
|
|
}
|
|
}
|