12. Integer to Roman

Given an integer, convert it to a roman numeral.

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

上网查了资料才知道怎么做……其实挺简单的，因为个、十、百、千的每一位都有对应的罗马数字表示：

class Solution {
public:
string intToRoman(int num) {
char* c[4][10]={
{"","I","II","III","IV","V","VI","VII","VIII","IX"},
{"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"},
{"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"},
{"","M","MM","MMM"}
};
string roman;
roman.append(c[3][num / 1000 % 10]);
roman.append(c[2][num / 100 % 10]);
roman.append(c[1][num / 10 % 10]);
roman.append(c[0][num % 10]);

return roman;
}
};