12. Integer to Roman C++

直接将各个数位上每个数所代表的罗马数字表示成字符串数组，然后提取出num的各位数，将对应的string相加

class Solution {
public:
    string intToRoman(int num) {
        string romanSingle[] = {"","I","II","III","IV","V","VI","VII","VIII","IX"};
        string romanTen[] = {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"};
        string romanHundred[] = {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"};
        string romanThousand[] = {"","M","MM","MMM","MMMM"};
        return romanThousand[num/1000] + romanHundred[(num%1000)/100]
            + romanTen[(num%100)/10] + romanSingle[num%10];
    }
};