題目：Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

I = 1;
V = 5;
X = 10;
L = 50;
C = 100;
D = 500;
M = 1000;

其中每兩個階段的之間有一個減法的表示，比如900=CM， C寫在M前面表示M-C。

範圍給到3999，感覺情況不多直接打表其實更快，用程式碼判斷表示估計比較繁瑣。

然後就是貪心的做法，每次選擇能表示的最大值，把對應的字串連起來。 

class Solution {
public:
    string intToRoman(int num) {
        string str;  
        string symbol[]={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};  
        int value[]=    {1000,900,500,400, 100, 90,  50, 40,  10, 9,   5,  4,   1}; 
        for(int i=0;num!=0;++i)
        {
            while(num>=value[i])
            {
                num-=value[i];
                str+=symbol[i];
            }
        }
        return str;
    }
};