QuestionC.java

package Q16_18_Pattern_Matcher;

public class QuestionC {
	
	public static String buildFromPattern(String pattern, String main, String alt) {	
		StringBuffer sb = new StringBuffer();
		char first = pattern.charAt(0);
		for (char c : pattern.toCharArray()) {
			if (c == first) {
				sb.append(main);
			} else {
				sb.append(alt);
			}
		}
		return sb.toString();
	}
	
	public static int countOf(String pattern, char c) {
		int count = 0;
		for (int i = 0; i < pattern.length(); i++) {
			if (pattern.charAt(i) == c) {
				count++;
			}
		}
		return count;
	}
	
	public static boolean doesMatch(String pattern, String value) {
		if (pattern.length() == 0) return value.length() == 0;
		
		char mainChar = pattern.charAt(0);
		char altChar = mainChar == 'a' ? 'b' : 'a';
		int size = value.length();

		int countOfMain = countOf(pattern, mainChar);
		int countOfAlt = pattern.length() - countOfMain;
		int firstAlt = pattern.indexOf(altChar);
		int maxMainSize = size / countOfMain;
		
		for (int mainSize = 0; mainSize <= maxMainSize; mainSize++) {
			int remainingLength = size - mainSize * countOfMain;
			String first = value.substring(0, mainSize);
			if (countOfAlt == 0 || remainingLength % countOfAlt == 0) {
				int altIndex = firstAlt * mainSize;
				int altSize = countOfAlt == 0 ? 0 : remainingLength / countOfAlt;
				String second = countOfAlt == 0 ? "" : value.substring(altIndex, altSize + altIndex);
				
				String candidate = buildFromPattern(pattern, first, second);
				
				if (candidate.equals(value)) {
					System.out.println(first + ", " + second);
					return true;
				}
			}
		}
		return false;	
	}
	
	public static void main(String[] args) {
		String[][] tests = {{"ababb", "backbatbackbatbat"}, {"abab", "backsbatbackbats"}, {"aba", "backsbatbacksbat"}};
		for (String[] test : tests) {
			String pattern = test[0];
			String value = test[1];
			System.out.println(pattern + ", " + value + ": " + doesMatch(pattern, value));
		}

	}

}