StringCompression.java

//http://coolcodebro.blogspot.com/2012/12/string-compression.html

public class StringCompression {
	public static void main(String[] args) {
		new StringCompression().run();
	}
	
	void run() {
		String str = "aabcccccaaa";
		String compr = compress(str);
		
		System.out.printf("Original: %s (%d)%n", str, str.length());
		System.out.printf("Compressed: %s (%d)%n", compr, compr.length());
	}
	
	String compress(String str) {
		if(str.length() < 3)
			return str;
		
		StringBuilder compressed = new StringBuilder();
		int count = 1;
		char prev = str.charAt(0), current;
		
		for(int i=1; i<str.length(); i++) {
			current = str.charAt(i);
			
			if(current != prev) {
				compressed.append(prev);
				compressed.append(count);
				
				prev = current;
				count = 1;
			}
			else
				count++;
		}
		
		//Add the last repeating character
		compressed.append(prev);
		compressed.append(count);
		
		if(compressed.length() < str.length())
			return compressed.toString();
		
		return str;
	}
}