IntegerToRoman.java

/*Seven different symbols represent Roman numerals with the following values:
Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000
Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules:
If the value does not start with 4 or 9, select the symbol of the maximal value that can be subtracted from the input, append that symbol to the result, subtract its value, and convert the remainder to a Roman numeral.
If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol, for example, 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM).
Only powers of 10 (I, X, C, M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V), 50 (L), or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form.
Given an integer, convert it to a Roman numeral.*/
import java.util.*;
class IntegerToRoman{
    public static String intToRoman(int num){
        if (num<=0 || num>3999){
            return "-1";
        }
        int[] values={1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        String[] symbols={"M", "CM", "D", "CD", "C", "XC","L", "XL", "X", "IX", "V", "IV", "I"};
        StringBuilder roman=new StringBuilder();
        for (int i=0;i<values.length && num>0;i++){
            while(num>=values[i]) {
                roman.append(symbols[i]);
                num-=values[i];
            }
        }
        return roman.toString();
    }
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        int num=sc.nextInt();
        System.out.println(intToRoman(num));
    }
}