---
title: Roman Numeral Converter
---
# Roman Numeral Converter
---
## Problem Explanation
You will create a program that converts an integer to a Roman Numeral.
#### Relevant Links
* Roman Numerals
* Array.splice()
* Array.indexOf()
* Array.join()
---
## Hints
### Hint 1
Creating two arrays, one with the Roman Numerals and one with the decimal equivalent for the new forms will be very helpful.
### Hint 2
If you add the numbers to the arrays that go before the new letter is introduced, like values for 4, 9, and 40, it will save you plenty of code.
### Hint 3
You can't have more than three consecutive Roman numerals together.
---
## Solutions
Solution 1 (Click to Show/Hide)
```javascript
var convertToRoman = function(num) {
var decimalValue = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1];
var romanNumeral = [
"M",
"CM",
"D",
"CD",
"C",
"XC",
"L",
"XL",
"X",
"IX",
"V",
"IV",
"I"
];
var romanized = "";
for (var index = 0; index < decimalValue.length; index++) {
while (decimalValue[index] <= num) {
romanized += romanNumeral[index];
num -= decimalValue[index];
}
}
return romanized;
};
// test here
convertToRoman(36);
```
#### Code Explanation
* We start off by creating two arrays with default conversion with matching indices. These are called `decimalValue` and `romanNumeral`. We also create an empty string variable, `romanized`, which will house the final roman number.
* Using a for loop, we loop through the indicies of the `decimalValue` array. We continue to loop until while the value at the current `index` will fit into `num`.
* Next, we add the roman numeral and decrease `num` by the decimal equivalent.
* Finally, we return the value of `romanized`.
#### Relevant Links
* For Loops
* While Loops
Solution 2 (Click to Show/Hide)
```javascript
function convertToRoman(num) {
var romans = ["I", "V", "X", "L", "C", "D", "M"],
ints = [],
romanNumber = [],
numeral = "";
while (num) {
ints.push(num % 10);
num = Math.floor(num / 10);
}
for (i = 0; i < ints.length; i++) {
units(ints[i]);
}
function units() {
numeral = romans[i * 2];
switch (ints[i]) {
case 1:
romanNumber.push(numeral);
break;
case 2:
romanNumber.push(numeral.concat(numeral));
break;
case 3:
romanNumber.push(numeral.concat(numeral).concat(numeral));
break;
case 4:
romanNumber.push(numeral.concat(romans[i * 2 + 1]));
break;
case 5:
romanNumber.push(romans[i * 2 + 1]);
break;
case 6:
romanNumber.push(romans[i * 2 + 1].concat(numeral));
break;
case 7:
romanNumber.push(romans[i * 2 + 1].concat(numeral).concat(numeral));
break;
case 8:
romanNumber.push(
romans[i * 2 + 1]
.concat(numeral)
.concat(numeral)
.concat(numeral)
);
break;
case 9:
romanNumber.push(romans[i * 2].concat(romans[i * 2 + 2]));
}
}
return romanNumber
.reverse()
.join("")
.toString();
}
// test here
convertToRoman(97);
```
#### Code Explanation
* Create an array of Roman Numerals (`romans`).
* Use a for loop to create an array of the digits (`ints`) in the number.
* Loop through the array of digits (base 10) and as you do, increment the Roman Numeral (base 5) index by 2 (`numeral = romans[i*2]`).
* Within the loop, use Switch Case to push the proper Roman Numerals (backwards) onto that array.
* Reverse the Roman Numerals array and turn it into a string.
#### Relevant Links
* For Loops
* While Loops
* Math
Solution 3 (Click to Show/Hide)
```javascript
function convertToRoman(num) {
var romans = [
// 10^i 10^i*5
["I", "V"], // 10^0
["X", "L"], // 10^1
["C", "D"], // 10^2
["M"] // 10^3
],
digits = num
.toString()
.split("")
.reverse()
.map(function(item, index) {
return parseInt(item);
}),
numeral = "";
// Loop through each digit, starting with the ones place
for (var i = 0; i < digits.length; i++) {
// Make a Roman numeral that ignores 5-multiples and shortening rules
numeral = romans[i][0].repeat(digits[i]) + numeral;
// Check for a Roman numeral 5-multiple version
if (romans[i][1]) {
numeral = numeral
// Change occurrences of 5 * 10^i to the corresponding 5-multiple Roman numeral
.replace(romans[i][0].repeat(5), romans[i][1])
// Shorten occurrences of 9 * 10^i
.replace(
romans[i][1] + romans[i][0].repeat(4),
romans[i][0] + romans[i + 1][0]
)
// Shorten occurrences of 4 * 10^i
.replace(romans[i][0].repeat(4), romans[i][0] + romans[i][1]);
}
}
return numeral;
}
// test here
convertToRoman(36);
```
#### Code Explanation
* Use an array (`romans`) to create a matrix containing the Roman numeral for a given power of 10 and, if available, the Roman numeral for that power of 10 times 5.
* Convert the input number (`num`) to a reversed array of digits (`digits`) so that we can loop through those digits starting with the ones position and going up.
* Loop through each digit, starting with the ones place, and create a Roman numeral string by adding each higher-power Roman numeral to the start of the `numeral` string a number of times equal to `digit`. This initial string ignores the Roman numerals that are a power of 10 times 5 and also ignores shortening rules.
* If the relevant power of 10 has a 5-multiple Roman numeral, in `numeral`, replace 5-in-a-row occurrences with the relevant 5-multiple Roman numeral (i.e., V, L, or D) and shorten occurrences of 9 * 10^i (e.g., VIIII to VIX) and 4 * 10^i (e.g., XXXX to XL). Order is important here!
* Finally, return `numeral`.
#### Relevant Links
* For Loops
* .split()
* .reverse()
* .map()
* .toString()
* parseInt()
* .replace()
* .repeat()