思路：

從大到小貪心

package Level2;

/**
 * Integer to Roman 
 * 
 *  Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.
 *
 */
public class S12 {

	public static void main(String[] args) {

	}
	
	public String intToRoman(int num) {
		if(num < 1 || num > 3999){  
            return "-1";  
        }  
   
        int[] aArray = {1000,900,500,400,100,90,50,40,10,9,5,4,1};  
        String[] rArray = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};  
        String rNumber = "";  
   
        for(int i=0; i<aArray.length; i++){  
            while(num >= aArray[i]){  
                rNumber += rArray[i];  
                num -= aArray[i];  
            }  
        }  
   
        return rNumber;  
    }

}