请将给出的整数转化为罗马数字
保证输入数字的范围在1 到 3999之间。 

示例1
输入
1
输出
"I"

首先搞清楚罗马数字，然后枚举出符号
I IV V IX X XL L XC C CD D CM M
1 4 5 9 10 40 50 90 100 400 500 900 1000
从后往前逐个比对就可以了 

public String intToRoman (int num) {      
    StringBuffer sb = new StringBuffer();         
    int[] s = new int[]{1,4,5,9,10,40,50,90,100,400,500,900,1000};         
    String[] st=new String[]{"I","IV","V","IX","X","XL","L","XC","C","CD","D","CM","M"};         
    for(int i =s.length-1;i>=0;){             
        if(num>=s[i]){                 
            sb=sb.append(st[i]);                 
            num-=s[i];             
        }else{                 
            i--;             
        }         
    }         
    return sb.toString();     
}