Why does the Roman to Integer conversion in JS only convert the first character?

Struggling with Leedcode question 13: Given a roman numeral, convert it to an integer. The input is guaranteed to be within the range from 1 to 3999. I've written some code below, but I'm puzzled as to why it only converts the first character in the roman numeral to an integer.

var romanToInt = function(s) {
  var result = 0;
  if (s == null) {
    result = 0;
  }
  var myMap = new Map();
  myMap.set('I', 1);
  myMap.set('V', 5);
  myMap.set('X', 10);
  myMap.set('L', 50);
  myMap.set('C', 100);
  myMap.set('D', 500);
  myMap.set('M', 1000);

  var len = s.length;
  for (var i = 0; i < len; i++) {
    if (myMap.get(s.charAt(i)) < myMap.get(s.charAt(i + 1))) {
      result -= myMap.get(s.charAt(i))
    } else {
      result += myMap.get(s.charAt(i))
    }
    return result;
  };
}

console.log(romanToInt('VI'));
console.log(romanToInt('V'));
console.log(romanToInt('VII'));

javascriptintegerroman-numerals

Answer №1

Due to the placement of

return result;

within the loop, it causes the loop to end after just one iteration. To fix this, simply move it down one line. Also, ensuring proper formatting can help avoid such mistakes altogether ;)

const values = new Map([
  ['I', 1],
  ['V', 5],
  ['X', 10]
  /*....*/
]);

function romanToInt(string) {
  let result = 0,
    current, previous = 0;
  for (const char of string.split("").reverse()) {
    current = values.get(char);
    if (current >= previous) {
      result += current;
    } else {
      result -= current;
    }
    previous = current;
  }
  return result;
}

console.log(romanToInt('I'));
console.log(romanToInt('II'));
console.log(romanToInt('III'));
console.log(romanToInt('IV'));
console.log(romanToInt('V'));
console.log(romanToInt('VI'));
console.log(romanToInt('VII'));
console.log(romanToInt('VIII'));
console.log(romanToInt('IX'));
console.log(romanToInt('X'));
console.log(romanToInt('XI'));
console.log(romanToInt('XII'));
console.log(romanToInt('XIII'));
console.log(romanToInt('XIV'));
console.log(romanToInt('XV'));
console.log(romanToInt('XVI'));
console.log(romanToInt('XVII'));
console.log(romanToInt('XVIII'));
console.log(romanToInt('XIX'));
console.log(romanToInt('XX'));

Answer №2

Ensure that your return result; statement is placed outside of the loop to avoid any issues.

Here is a more simplified version of your code for better readability:

const myMap=new Map();
myMap.set('I', 1);
myMap.set('V', 5);
myMap.set('X', 10);
myMap.set('L', 50);
myMap.set('C', 100);
myMap.set('D', 500);
myMap.set('M', 1000);

var romanToInt = function(s) {
   var result=0;
   if(s){
     var s1=s.split('');
     s1.forEach(function(e,i){
          result += myMap.get(e) < myMap.get(s1[i+1]) ? -myMap.get(e) : myMap.get(e);  // using ternary operator with '-' where necessary
     });
   }
   return result; // make sure it's outside the loop
}
console.log(romanToInt('IV'));
console.log(romanToInt('V'));
console.log(romanToInt('VII'));

Answer №3

Initially, I define the romanVal as an object that holds the values of all Roman symbols. Then, I set the result to zero in the next step. I check for an empty user input with the statement if (s === '') return;. If the input is empty, the result is set to 0. Otheriwse, I convert the input into an array and iterate through each element, converting them to numbers and storing them in the inputval array. Finally, I loop through this array to determine whether to add or subtract the element at index i based on the comparison with the next element.

var romanToInt = function (s) {
    let romanVal = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
    let result = 0;
    if (s === '') return;
    let inputs = Array.of(...s);
    let inputsVal = [];
    inputs.map((e) => ((e = romanVal[e]), inputsVal.push(e)));
    for (let i = 0; i < inputsVal.length; i++) {
        inputsVal[i] < inputsVal[i + 1]
            ? (result -= inputsVal[i])
            : (result += inputsVal[i]);
    }
    return result;
};

romanToInt('III')

Answer №4

Here is a shortened version of the Roman to Integer problem:

const romanToInt = (str) => {
  const roman = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
  let num = 0;
  for (let i = 0; i < str.length; i++) {
    const curr = roman[str[i]];
    const next = roman[str[i + 1]];
    (curr < next) ? (num -= curr) : (num += curr);
  }
  return num;
};

console.log(romanToInt('IV'));
console.log(romanToInt('VIII'));
console.log(romanToInt('LXXIX'));
console.log(romanToInt('MCMXLIV'));

Here is another innovative approach from @Jin150Job

const romanToInt = (str) => {
  const roman = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
  let num = 0;
  if (str.includes('CM')) num -= 200;
  if (str.includes('CD')) num -= 200;
  if (str.includes('XC')) num -= 20;
  if (str.includes('XL')) num -= 20;
  if (str.includes('IX')) num -= 2;
  if (str.includes('IV')) num -= 2;
  for (let i = 0; i < str.length; i++) {
    num += roman[str[i]];
  }
  return num;
};

console.log(romanToInt('IV'));
console.log(romanToInt('VIII'));
console.log(romanToInt('LXXIX'));
console.log(romanToInt('MCMXLIV'));

Answer №5

An elegant and efficient solution to convert Roman numerals to integers:

def roman_to_int(s: str) -> int: 
    roman_dict = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000} 
    result = 0
    prev_value = 0
    
    for c in reversed(s):
        current_value = roman_dict[c]
        if current_value >= prev_value:
            result += current_value
        else:
            result -= current_value
        prev_value = current_value
        
    return result

Answer №6

Here is a different approach for converting Roman numerals to integers:

function romanToInt(romanNumeral) {
   let currentValue = 0;
    let result = 0;
    const letters = romanNumeral.split('');
    const romanNumeralValues = {
      I: 1,
      V: 5,
      X: 10,
      L: 50,
      C: 100,
      D: 500,
      M: 1000,
    };
    let firstValue = romanNumeralValues[letters[0].toUpperCase()];
    for (let letter of letters) {
      currentValue = romanNumeralValues[letter.toUpperCase()];
      if (currentValue <= firstValue) {
        result += currentValue;
      } else {
        result = currentValue - result;
      }
    }
    console.log(`Roman Numeral: ${romanNumeral}\nInteger Value: ${result} \n \n`);
    return result;
}

romanToInt('I');
romanToInt('IV');
romanToInt('VI');
romanToInt('IX');
romanToInt('X');
romanToInt('XI');
romanToInt('XII');
romanToInt('XL');
romanToInt('LV');
romanToInt('MMM');
romanToInt('MMC');
romanToInt('MMc');

Answer №7

   const romanNumerals = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
   let total = 0;
   for (let i = 0; i < romanString.length; i++) {
     const current = romanNumerals[romanString[i]];
     const next = romanNumerals[romanString[i + 1]];
     if (current < next) {
       total -= current;
     } else {
       total += current;
     }
   }
   return total;
 };

 const romanNumber = romanToInteger("MCMXCIV");
 console.log(romanNumber);

Answer №8

    function romanToNumber(romanNumeral) {
    const romanValues = {
        I: 1,
        V: 5,
        X: 10,
        L: 50,
        C: 100,
        D: 500,
        M: 1000
    };

    let result = 0;

    for (let i = 0; i < romanNumeral.length; i++) {
        const current = romanValues[romanNumeral[i]];
        const next = romanValues[romanNumeral[i + 1]];

        if (current < next) {
            result -= current;
        } else {
            result += current;
        }
    }

    return result;
}

// Test cases:
console.log(romanToNumber("III"));       // Output: 3
console.log(romanToNumber("LVIII"));     // Output: 58
console.log(romanToNumber("MCMXCIV"));   // Output: 1994

Answer №9

Here is a suggestion for you to consider:

function convertRomanNumeralToInteger(romanNumeral) {
   if(typeof romanNumeral !== 'string') return NaN;
   const romanRegExp = /^(?=[MDCLXVI])(M*)(?:(C)(?:(D)|(M))|(D?)(C{0,3}))(?:(X)(?:(L)|(C))|(L?)(X{0,3}))(?:(I)(?:(V)|(X))|(V?)(I{0,3}))$/i;
   let parts = romanNumeral.match(romanRegExp);
   if(!parts) return NaN;
   let result = 0;
   [0, 1000, -100,500,1000,500,100, -10,50,100,50,10, -1,5,10,5,1].forEach(
      (weight, i) => result += weight * (parts[i] || '').length
   );
   return result;
}

console.log(convertRomanNumeralToInteger('IV'));
console.log(convertRomanNumeralToInteger('MMXIX'));

Answer №10

Why not give this a try? It might just do the trick:


<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function romanToDecimal(input) {
  const romanNumerals = input.split('');
  const values = {
    I: 1,
    V: 5,
    X: 10,
    L: 50,
    C: 100,
    D: 500,
    M: 1000,
  };

  let sum = 0;
  for (let i = 0; i < romanNumerals.length; i += 1) {
    if (values[romanNumerals[i]] < values[romanNumerals[i + 1]]) {
      sum += values[romanNumerals[i + 1]] - values[romanNumerals[i]];
      i += 1;
    } else {
      sum += values[romanNumerals[i]];
    }
  } return sum;
}
      
console.log(romanToDecimal("VIII"));
console.log(romanToDecimal("LXXIX"));
console.log(romanToDecimal("MCMXLIV"));

Answer №11

** this algorithm is applicable to all Roman numerals less than 3600

function romanToDecimal(romanNumeral) {
    const romanMap = {I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000};
    let total = 0;
    for (let i=0; i<romanNumeral.length; i++) {
        const value = romanMap[romanNumeral[i]];
        let nextValue;
        if (i+1 < romanNumeral.length) {
            // There is another character
            nextValue = romanMap[romanNumeral[i+1]];
            if (value >= nextValue) {
                total += value;
            } else {
                // Subtract the current value from the next value
                total += nextValue - value;
                i+=1;
            }
        } else {
            // Last character
            total += value;
        }
    }
    return total;
}

testing the function:

// TEST
romanToDecimal('MMMDXCIX')
=3599

Answer №12

function romanToInteger(s) {
    const romanMap = new Map();
    romanMap.set("I", 1);
    romanMap.set("V", 5);
    romanMap.set("X", 10);
    romanMap.set("L", 50);
    romanMap.set("C", 100);
    romanMap.set("D", 500);
    romanMap.set("M", 1000);
    romanMap.set("IV", 4);
    romanMap.set("IX", 9);
    romanMap.set("XL", 40);
    romanMap.set("XC", 90);
    romanMap.set("CD", 400);
    romanMap.set("CM", 900);
    
    if(s.length == 1){
        return romanMap.get(s);
    }
    
    let totalSum = 0;
    
    for(let i = 0; i < s.length;){
        const doubleValue = romanMap.get(s[i]+s[i+1]);
        
        if(doubleValue == undefined){
            totalSum += romanMap.get(s[i]);
            i++;
        }else{
            totalSum += doubleValue;
            i+=2;
        }        
    }
    
    return totalSum;
}

Answer №13

function convertRomanToNumber(romanNumeral) {
   let romanNumerals= { I : 1,  V : 5, X : 10, L : 50, C : 100,  D : 500, M :1000 };
   function checkSubtractionRule(currNumeral, nextNumeral) {
      if(currNumeral === nextNumeral) return false;
      if(romanNumerals[currNumeral] < romanNumerals[nextNumeral]) return true; 
      return false;
   }
   let numeralArr = romanNumeral.split('');
   let total = 0;
   for(let i=0; i < numeralArr.length; i++){
       if(checkSubtractionRule(numeralArr[i],numeralArr[i+1]) && i < numeralArr.length - 1) {
          total = total + (romanNumerals[numeralArr[i+1]] - romanNumerals[numeralArr[i]]);
          i++;
       } else {
          total = total + romanNumerals[numeralArr[i]]; 
       }
   }
   return total;
}

console.log(convertRomanToNumber('XIX'));

Answer №14

Convert Roman Numerals to Integers (frequently asked in interviews with a provided solution) . The solution utilizes string manipulation techniques.

var romanToInt = function (s) {
      let roman = { "I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000 }, sum = 0;
      if (roman[s]) {
        return roman[s];
      }
      else {
        for (let i = s.length - 1; i >= 0; i--) {
          if (s.charAt(i - 1) && roman[s.charAt(i - 1)] < roman[s.charAt(i)]) {
            sum += roman[s.charAt(i)] - roman[s.charAt(i - 1)];
            i--;
          } else {
            sum += roman[s.charAt(i)]
          }
        }
        return sum;
      }
    };
    romanToInt('IV');

Answer №15

This solution has proven to be effective

var romanToInt = function(s) {
    const main = {
        'I':1,
        'V':5,
        'X':10,
        'L':50,
        'C':100,
        'D':500,
        'M':1000,
    }
    var returnValue = 0;
    for(let i = 0 ; i < s.length; i++){
        const currentValue = main[s[i]];
        const nextValue = main[s[i+1]];

        !!!nextValue ? returnValue += currentValue :
        currentValue === nextValue ? returnValue += currentValue :
        currentValue > nextValue ? returnValue += currentValue : returnValue -= currentValue
    }
    return returnValue
};

//1994
console.log(romanToInt('MCMXCIV'))

Answer №16

Check out this example that utilizes the reduce method

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

const convertToNumber = romanNumeral => {
  const romanDigits = romanNumeral.split('')

  return romanDigits.reduce(
    (acc, curr, index) =>
      romanNumerals[curr] < romanNumerals[romanDigits[index + 1]]
        ? acc - romanNumerals[curr]
        : acc + romanNumerals[curr],
    0
  )
}

console.log(convertToNumber('XXXIX'))
console.log(convertToNumber('XL'))
console.log(convertToNumber('MMXXI'))
console.log(convertToNumber('CLX'))
console.log(convertToNumber('DCCLXXXIX'))
console.log(convertToNumber('MCMXVIII'))
console.log(convertToNumber('MMMCMXCIX'))

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