menu.java

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class menu {
    
	public static void main(String[] args) {
		
		HDC hdc = new HDC();
		Scanner scanner = new Scanner(System.in);
		System.out.print( "Input to encode > " );
		String input = scanner.nextLine();
		
		int c = 0;
		do {
			System.out.println( "------------------------------" );
			System.out.println( "   1. Run in one-step-only" );
			System.out.println( "   2. Exit" );
			System.out.println( "------------------------------" );
			System.out.println( "Please input your choice (1-2):" );
			c = scanner.nextInt();
			
			if( c == 1 ) {
				String encoded = hdc.compress(input);
				System.out.println( "The encoded result:" );
				System.out.println( encoded );
				
				hdc.echoNodes();
				
				System.out.println( "Statistic" );
				System.out.println( "size of input: " + input.length() );
				System.out.println( "size of output: " + encoded.length() );
				System.out.println( "compression ratio: " + ((float)input.length() - (float)encoded.length())/(float)input.length() + "%");
				System.out.println( "average code length: " + (float)encoded.length()/(float)hdc.encodedNodes.size());
				System.out.println( "entropy: ");
			} 
			
			
		} while( c != 2 );
	}
}

class HDC {
	List<String> encodedNodes= new ArrayList<String>();
	
	public String compress(String str) {
		String result = "";
		List<String> nodes= new ArrayList<String>();
		Pattern pattern = Pattern.compile("(.)\\1{1,}");
		Matcher m = pattern.matcher(str);
		int offset = 0;
		while( m.find() ) {
			int start = m.start();
			int end = m.end();
			
			// Ouput non repeat
			if( offset < start ) {
				nodes.add(str.substring(offset, start));
			}
			
			nodes.add(str.substring(start, end));
			offset = end;
		}
		
		if( offset == 0 ) {
			nodes.add(str);
		} else if( offset != str.length() ) {
			nodes.add(str.substring(offset, str.length()));
		}
		
		for( String s : nodes ) {
			if(s.isEmpty()) continue;
			if(s.length() == 1 || s.charAt(0) != s.charAt(1)) {
				String e = "n" + s.length() + s;
				result += e;
				this.encodedNodes.add(e);
			}
			else {
				String e = "r" + s.length() + s.charAt(0);
				result += e;
				this.encodedNodes.add(e);
			}
		};
		
		return result;
	}
	
	public void echoNodes() {
		System.out.println( "Where" );
		for( String s : encodedNodes) {
			String code = "";
			int number = Integer.parseInt(String.valueOf(s.charAt(1)));
			if( s.charAt(0) == 'r' ) {
				for( int i = 0; i < number; ++i ) {
					code += s.charAt(2);
				}
			} else if (s.charAt(0) == 'n') {
				for( int i = 0; i < number; ++i ) {
					code += s.charAt(number + 1);
				}
			}
			System.out.println( s + ":" + code );
		}
	}
}