Roman Numerals Decoder

Roman Numerals Decoder

Roman Numerals DecoderCodewars

Approach

Find pattern

left-hand side value should subtract from right-hand side value when left value lower than right value

solve the problem

1. convert all roman number to decimal number and split as a array

2. check all of the array that LHS is greater than RHS

3. if LHS value lower than RHS add to restValue and remove that value from array repeat from 2

4. summation filtered array values

5. subtract restValue from 4.

6. return the result

JavaScript

// roman-numerals-decoder
// Roman Numerals Decoder
// https://www.codewars.com/kata/51b6249c4612257ac0000005/

const romanSymbolMap = {
  I: 1,
  V: 5,
  X: 10,
  L: 50,
  C: 100,
  D: 500,
  M: 1000,
};

const solution = (roman) => {
  let convertedNumbers = roman.split('').map((v) => romanSymbolMap[v]);
  let hasMixedValue = false;
  let targetValue = 0;
  let restValue = 0;
  
  do {
    hasMixedValue = false;
    
    convertedNumbers.reduce((acc, cur) => {
      if (acc < cur) {
        hasMixedValue = true;
        targetValue = cur;
      }
      return cur;
    });
    
    if (hasMixedValue) {
      restValue += convertedNumbers.filter((v) => v < targetValue).reduce((acc, cur) => acc + cur);
      convertedNumbers = convertedNumbers.filter((v) => v >= targetValue);
    }
  } while (hasMixedValue);
  
  return convertedNumbers.reduce((acc, cur) => acc + cur) - restValue;
};


// test code
console.log(solution('XXI'), 21);
console.log(solution('I'), 1);
console.log(solution('IV'), 4);
console.log(solution('MMVIII'), 2008);
console.log(solution('MDCLXVI'), 1666);