Assignment finished

src/RomanNumerals.java

@@ -1,8 +1,233 @@
-
 public class RomanNumerals {
-	public int convertToInteger(String romanNum) {
-		// To be Implemented
-		return 0;
+
+	public int convertToInteger(String romanNum) throws RomanNumeralsException {
+
+		int sum = 0;
+
+		if(checkInput(romanNum)) {
+
+			if(check_IXCM_3_times(romanNum)) {
+
+				if(check_VLD_Once(romanNum)) {
+
+					if(check_substraction_rule(romanNum)) {
+
+						if(check_one_substraction(romanNum)) {
+
+							for(int i = romanNum.length() - 1; i >= 0; i--) {
+
+								if(i != 0 && letterValue(romanNum.charAt(i)) > letterValue(romanNum.charAt(i - 1))) {
+
+									sum = sum + letterValue(romanNum.charAt(i)) - 2 * letterValue(romanNum.charAt(i - 1));
+
+								}
+
+								else {
+
+									sum += letterValue(romanNum.charAt(i));
+
+								}
+
+							}
+
+						}
+
+					}
+
+				}
+
+			}
+
+		}
+
+		return sum;
+
+	}
+
+	public int letterValue(char letter) throws RomanNumeralsException {
+
+		int value = -1;
+
+		switch(letter) {
+
+		case 'I':
+
+			value = 1;
+			break;
+
+		case 'V':
+
+			value = 5;
+			break;
+
+		case 'X':
+
+			value = 10;
+			break;
+
+		case 'L':
+
+			value = 50;
+			break;
+
+		case 'C':
+
+			value = 100;
+			break;
+
+		case 'D':
+
+			value = 500;
+			break;
+
+		case 'M':
+
+			value = 1000;
+			break;
+
+		default:
+
+			throw new RomanNumeralsException();
+
+
+		}
+
+		return value;
+
+	}
+
+	public boolean checkInput(String RomanNum) throws RomanNumeralsException {
+
+		for(int i = 0; i < RomanNum.length(); i++) {
+
+			letterValue(RomanNum.charAt(i));
+
+		}
+
+		return true;
+
+	}
+
+	public boolean check_IXCM_3_times(String RomanNum) throws RomanNumeralsException {
+
+		char previousLetter = ' ';
+		int count = 0;
+
+		for(int i = 0; i < RomanNum.length(); i++) {
+
+			if(RomanNum.charAt(i) == 'I' || RomanNum.charAt(i) == 'X' || RomanNum.charAt(i) == 'C' || RomanNum.charAt(i) == 'M') {
+
+				if(RomanNum.charAt(i) == previousLetter) {
+
+					count++;
+
+				}
+
+				else {
+
+					count = 1;
+
+					previousLetter = RomanNum.charAt(i);
+
+				}
+
+			}
+
+			if(count > 3) {
+
+				throw new RomanNumeralsException();
+
+			}
+
+		}
+
+		return true;
+
+
+	}
+
+	public boolean check_VLD_Once(String RomanNum) throws RomanNumeralsException {
+
+		char previousLetter = ' ';
+		int count = 0;
+
+		for(int i = 0; i < RomanNum.length(); i++) {
+
+			if(RomanNum.charAt(i) == 'V' || RomanNum.charAt(i) == 'L' || RomanNum.charAt(i) == 'D') {
+
+				if(RomanNum.charAt(i) == previousLetter) {
+
+					count++;
+
+				}
+
+				else {
+
+					count = 1;
+
+					previousLetter = RomanNum.charAt(i);
+
+				}
+
+			}
+
+			if(count > 1) {
+
+				throw new RomanNumeralsException();
+
+			}
+
+		}
+
+		return true;
+
+
+	}
+
+	public boolean check_substraction_rule(String RomanNum) throws RomanNumeralsException {
+
+		for(int i = 0; i < RomanNum.length() - 1; i++) {
+
+			if(letterValue(RomanNum.charAt(i)) < letterValue(RomanNum.charAt(i + 1))) {
+
+				if(letterValue(RomanNum.charAt(i)) > 10 * letterValue(RomanNum.charAt(i + 1))) {
+
+					throw new RomanNumeralsException();
+
+				}
+
+				if(RomanNum.charAt(i) == 'V' || RomanNum.charAt(i) == 'L' || RomanNum.charAt(i) == 'D') {
+
+					throw new RomanNumeralsException();
+
+				}
+
+			}
+
+		}
+
+		return true;
+
+	}
+
+	public boolean check_one_substraction(String RomanNum) throws RomanNumeralsException {
+
+		for(int i = 0; i < RomanNum.length() - 2; i++) {
+
+			if(letterValue(RomanNum.charAt(i)) == letterValue(RomanNum.charAt(i + 1))) {
+
+				if(letterValue(RomanNum.charAt(i + 1)) < letterValue(RomanNum.charAt(i + 2))) {
+
+					throw new RomanNumeralsException();
+
+				}
+
+			}
+
+		}
+
+		return true;
 
 	}
+
 }

src/RomanNumeralsException.java

@@ -0,0 +1,10 @@
+
+public class RomanNumeralsException extends Exception{
+
+	public RomanNumeralsException() {
+
+		System.out.println("Wrong format : correct roman number format required. Please check the rules.");
+
+	}
+
+}