Write a number in Roman numerals
A film credit or a chapter heading wants MCMXCIV rather than 1994.
- The subtractive forms count: 4 is IV, 9 is IX, 40 is XL, 90 is XC, 400 is CD, 900 is CM.
- Only 1 to 3999 can be written; anything outside gives an empty string.
toRoman(amount: int) → string
C++ needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
std::string toRoman(int amount) {
}Worked examples
| Call | Result |
|---|---|
toRoman(1) | std::string("I") |
toRoman(4) | std::string("IV") |
toRoman(14) | std::string("XIV") |
toRoman(1994) | std::string("MCMXCIV") |
Hint
Keep the values and their symbols in one descending table, including the subtractive pairs. Then it is one greedy pass.
Reference solution in C++
std::string toRoman(int amount) {
if (amount < 1 || amount > 3999) return "";
int vals[13] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
const char* syms[13] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
int n = amount;
string result;
for (int i = 0; i < 13; i++) {
while (n >= vals[i]) { result += syms[i]; n -= vals[i]; }
}
return result;
}