freecodecamp: Roman Numeral Converter

RomanNumeralConverter.md

Description

Convert the given number into a roman numeral. All roman numerals answers should be provided in upper-case.

Tests

tests:
  - text: <code>convertToRoman(2)</code> should return "II".
    testString: assert.deepEqual(convertToRoman(2), "II");
  - text: <code>convertToRoman(3)</code> should return "III".
    testString: assert.deepEqual(convertToRoman(3), "III");
  - text: <code>convertToRoman(4)</code> should return "IV".
    testString: assert.deepEqual(convertToRoman(4), "IV");
  - text: <code>convertToRoman(5)</code> should return "V".
    testString: assert.deepEqual(convertToRoman(5), "V");
  - text: <code>convertToRoman(9)</code> should return "IX".
    testString: assert.deepEqual(convertToRoman(9), "IX");
  - text: <code>convertToRoman(12)</code> should return "XII".
    testString: assert.deepEqual(convertToRoman(12), "XII");
  - text: <code>convertToRoman(16)</code> should return "XVI".
    testString: assert.deepEqual(convertToRoman(16), "XVI");
  - text: <code>convertToRoman(29)</code> should return "XXIX".
    testString: assert.deepEqual(convertToRoman(29), "XXIX");
  - text: <code>convertToRoman(44)</code> should return "XLIV".
    testString: assert.deepEqual(convertToRoman(44), "XLIV");
  - text: <code>convertToRoman(45)</code> should return "XLV"
    testString: assert.deepEqual(convertToRoman(45), "XLV");
  - text: <code>convertToRoman(68)</code> should return "LXVIII"
    testString: assert.deepEqual(convertToRoman(68), "LXVIII");
  - text: <code>convertToRoman(83)</code> should return "LXXXIII"
    testString: assert.deepEqual(convertToRoman(83), "LXXXIII");
  - text: <code>convertToRoman(97)</code> should return "XCVII"
    testString: assert.deepEqual(convertToRoman(97), "XCVII");
  - text: <code>convertToRoman(99)</code> should return "XCIX"
    testString: assert.deepEqual(convertToRoman(99), "XCIX");
  - text: <code>convertToRoman(400)</code> should return "CD"
    testString: assert.deepEqual(convertToRoman(400), "CD");
  - text: <code>convertToRoman(500)</code> should return "D"
    testString: assert.deepEqual(convertToRoman(500), "D");
  - text: <code>convertToRoman(501)</code> should return "DI"
    testString: assert.deepEqual(convertToRoman(501), "DI");
  - text: <code>convertToRoman(649)</code> should return "DCXLIX"
    testString: assert.deepEqual(convertToRoman(649), "DCXLIX");
  - text: <code>convertToRoman(798)</code> should return "DCCXCVIII"
    testString: assert.deepEqual(convertToRoman(798), "DCCXCVIII");
  - text: <code>convertToRoman(891)</code> should return "DCCCXCI"
    testString: assert.deepEqual(convertToRoman(891), "DCCCXCI");
  - text: <code>convertToRoman(1000)</code> should return "M"
    testString: assert.deepEqual(convertToRoman(1000), "M");
  - text: <code>convertToRoman(1004)</code> should return "MIV"
    testString: assert.deepEqual(convertToRoman(1004), "MIV");
  - text: <code>convertToRoman(1006)</code> should return "MVI"
    testString: assert.deepEqual(convertToRoman(1006), "MVI");
  - text: <code>convertToRoman(1023)</code> should return "MXXIII"
    testString: assert.deepEqual(convertToRoman(1023), "MXXIII");
  - text: <code>convertToRoman(2014)</code> should return "MMXIV"
    testString: assert.deepEqual(convertToRoman(2014), "MMXIV");
  - text: <code>convertToRoman(3999)</code> should return "MMMCMXCIX"
    testString: assert.deepEqual(convertToRoman(3999), "MMMCMXCIX");

Solution

The offical soln:

function convertToRoman(num) {
  var ref = [['M', 1000], ['CM', 900], ['D', 500], ['CD', 400], ['C', 100], ['XC', 90], ['L', 50], ['XL', 40], ['X', 10], ['IX', 9], ['V', 5], ['IV', 4], ['I', 1]];
  var res = [];
  ref.forEach(function(p) {
    while (num >= p[1]) {
      res.push(p[0]);
      num -= p[1];
    }
  });
  return res.join('');
}

My soln:

function convertToRoman(num) {
//Break the number into Thousands, Hundreds, Tens and Ones, and write down each in turn.
//get the digits
const numStr=num.toString();
const len=numStr.length;
let Thousands=0,Hundreds= 0,Tens= 0;
if(len>=2){Tens=parseInt(numStr[len-1-1]);}
if(len>=3){Hundreds=parseInt(numStr[len-1-2]);}
if(len==4){Thousands=parseInt(numStr[0]);}
const Ones=num%10;
const lookup=[
    ["","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"]];
return lookup[3][Thousands]+lookup[2][Hundreds]+
lookup[1][Tens]+lookup[0][Ones];
}

convertToRoman(36);

My solution is the simplest and basic one.
Below are the more advance solutions given by the freecodecamp guide:
Soln 1:

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;
};

Soln 2:

References

fastest way to select the nth digit in integer in javascript?
freeCodeCamp Challenge Guide: Roman Numeral Converter
Roman Numeral Converter - A PEN BY Andy

Explanation of method 1 provided in freecodecamp guide:
Roman Numeral Converter - Hugh Winchester
Roman Numerals Converter - Jack Lyons