11 KiB
11 KiB
title |
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Roman Numeral Converter |
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Problem Explanation:
You will create a program that converts an integer to a Roman Numeral.
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Hint: 1
Creating two arrays, one with the Roman Numerals and one with the decimal equivalent for the new forms will be very helpful.
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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.
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Hint: 3
You can't have more than three consecutive Roman numerals together.
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Spoiler Alert!
Solution ahead!
Basic Code Solution:
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
andromanNumeral
. 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 currentindex
will fit intonum
. - Next, we add the roman numeral and decrease
num
by the decimal equivalent. - Finally, we return the value of
romanized
.
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- For Loops
- While Loops
Intermediate Code Solution:
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.
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Intermediate Code Solution:
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 todigit
. 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
.
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