A roman number or an empty string if the given number could not be converted.
assert(toRoman(1) == "I"); assert(toRoman(3) == "III"); assert(toRoman(4) == "IV"); assert(toRoman(5) == "V"); assert(toRoman(9) == "IX"); assert(toRoman(10) == "X"); assert(toRoman(33) == "XXXIII"); assert(toRoman(1111) == "MCXI"); assert(toRoman(1999) == "MCMXCIX"); assert(toRoman(550) == "DL"); assert(toRoman(400) == "CD"); assert(toRoman(40) == "XL"); // invalid assert(toRoman(0) == "");
Converts an integer to a roman number.