QuestionD.java

package Q16_18_Pattern_Matcher;

public class QuestionD {
	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;
			if (countOfAlt == 0 || remainingLength % countOfAlt == 0) {
				int altIndex = firstAlt * mainSize;
				int altSize = countOfAlt == 0 ? 0 : remainingLength / countOfAlt;
				if (matches(pattern, value, mainSize, altSize, altIndex)) {
					return true;
				}
			}
		}
		return false;
	}	
	
	public static boolean matches(String pattern, String value, int mainSize, int altSize, int firstAlt) {
		int stringIndex = mainSize;
		for (int i = 1; i < pattern.length(); i++) {
			int size = pattern.charAt(i) == pattern.charAt(0) ? mainSize : altSize;
			int offset = pattern.charAt(i) == pattern.charAt(0) ? 0 : firstAlt;
			if (!isEqual(value, offset, stringIndex, size)) {
				return false;
			}
			stringIndex += size;
		}
		return true;
	}
	
	public static boolean isEqual(String s1, int offset1, int offset2, int size) {
		for (int i = 0; i < size; i++) {
			if (s1.charAt(offset1 + i) != s1.charAt(offset2 + i)) {
				return false;
			}
		}
		return true;
	}
	
	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 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));
		}

	}

}