CC_1_5

StringCompress.java

// Cracking the Coding Interview
// 1.5 Implement a method to perform basic string compression using the counts of repeated characters. 
// For example, the string aabcccccaaa would become a2blc5a3. 
// If the "compressed" string would not become smaller than the original string, your method should return the original string.

class StringCompress {
	public static String compressString(String s) {
		if (s == null) return null;

		boolean needCompressing = false;
		for(int i = 0; i < s.length(); i++) {
			int dupNum = countDuplicateChar(s, i);
			if (dupNum > 1) {
				needCompressing = true;
				break;
			}
			i += dupNum;
		}
		if (needCompressing) {
			StringBuffer b = new StringBuffer();
			for(int i = 0; i < s.length(); i++) {
				int dupNum = countDuplicateChar(s, i);
				b.append(s.charAt(i));
				if (dupNum > 0) {
					b.append(dupNum+1);
				} 
				i += dupNum;
			}
			return b.toString();
		} else {
			return s;
		}
	}
	private static int countDuplicateChar(String s, int start) {
		int count = 0;
		for(int i = start+1; i < s.length(); i++) {
			if (s.charAt(i) == s.charAt(start)) {
				count++;
			} else {
				return count;
			}
		}
		return count;
	}

	public static void main(String[] args) {
		assert "".equals(compressString(""));
		assert compressString(null) == null;
		assert "a".equals(compressString("a"));
		assert "ab".equals(compressString("ab"));
		assert "abb".equals(compressString("abb"));
		assert "aa".equals(compressString("aa"));
		assert "ab3c2".equals(compressString("abbbcc"));
		assert " 4".equals(compressString("    "));

		System.out.println("Test Passed");
	}
}