TCSInterviewTest

import junit.framework.TestCase;

public class TCSInterviewTest extends TestCase {

    private static String transform(final String input) {

        final StringBuilder result = new StringBuilder(input.length());

        int charCount = 0;
        char lastChar = (char) -1;

        for (char thisChar : input.toCharArray()) {
            if (thisChar == lastChar) {
                ++charCount;
            } else {
                appendCharacterCount(result, lastChar, charCount);
                charCount = 1;
                lastChar = thisChar;
            }
        }

        appendCharacterCount(result, lastChar, charCount);

        return result.toString();
    }

    private static void appendCharacterCount(final StringBuilder result, final char chr, final int count) {
        if (count > 0) {
            result.append(chr);
            if (count > 1) {
                result.append(count);
            }
        }
    }

    public void testInterviewExample() {
        assertEquals("a3b2Bc2d3", transform("aaabbBccddd"));
    }

    public void testEmptyString() {
        assertEquals("", transform(""));
    }

    public void testOneChar() {
        assertEquals("x", transform("x"));
    }

    public void testTwoChar() {
        assertEquals("x2", transform("xx"));
    }

    public void testThreeChar() {
        assertEquals("x3", transform("xxx"));
    }

    public void testThreeUnique() {
        assertEquals("xyz", transform("xyz"));
    }

    public void testXYZZY() {
        assertEquals("xyz2y", transform("xyzzy"));
    }

}