Roman to Integer Conversion in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the result variable to zero.

DSA Javascript

function romanToInt(s) {
  let result = [1];
  return result;
}

Drag options to blanks, or click blank then click option'

A0

B1

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing result with 1 or null causes incorrect calculations.

Leaving result undefined leads to errors when adding values.

The result variable should start at 0 to accumulate the integer value.

2fill in blank

medium

Complete the code to get the integer value for the Roman numeral 'I' from the map.

DSA Javascript

const romanMap = {I: 1, V: 5, X: 10};
function romanToInt(s) {
  let result = 0;
  for (let i = 0; i < s.length; i++) {
    let value = romanMap[[1]];
  }
  return result;
}

Drag options to blanks, or click blank then click option'

Ai

Bs

Cs[i]

DromanMap[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using i directly instead of s[i] causes undefined values.

Using romanMap[i] is incorrect because i is an index, not a Roman numeral.

We use s[i] to get the current Roman numeral character from the string.

3fill in blank

hard

Fix the error in the if condition to check if the current Roman numeral value is less than the next one.

DSA Javascript

const romanMap = {I: 1, V: 5, X: 10};
function romanToInt(s) {
  let result = 0;
  for (let i = 0; i < s.length; i++) {
    let current = romanMap[s[i]];
    let next = romanMap[s[i + 1]];
    if (current [1] next) {
      result -= current;
    } else {
      result += current;
    }
  }
  return result;
}

Drag options to blanks, or click blank then click option'

A<

B>

C===

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' reverses the logic and causes wrong results.

Using '===' or '!==' does not compare sizes and breaks the logic.

If the current value is less than the next, we subtract it according to Roman numeral rules.

4fill in blank

hard

Fill both blanks to correctly handle the loop and avoid accessing undefined next character.

DSA Javascript

const romanMap = {I: 1, V: 5, X: 10};
function romanToInt(s) {
  let result = 0;
  for (let i = 0; i [1] s.length [2] 1; i++) {
    let current = romanMap[s[i]];
    let next = romanMap[s[i + 1]];
    if (current < next) {
      result -= current;
    } else {
      result += current;
    }
  }
  return result;
}

Drag options to blanks, or click blank then click option'

A<

B<=

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' causes out of bounds error when accessing s[i + 1].

Using '+' instead of '-' causes incorrect loop range.

The loop runs while i is less than s.length minus 1 to safely access s[i + 1].

5fill in blank

hard

Fill the blank to add the last Roman numeral value after the loop ends.

DSA Javascript

const romanMap = {I: 1, V: 5, X: 10};
function romanToInt(s) {
  let result = 0;
  for (let i = 0; i < s.length - 1; i++) {
    let current = romanMap[s[i]];
    let next = romanMap[s[i + 1]];
    if (current < next) {
      result -= current;
    } else {
      result += current;
    }
  }
  result += romanMap[[1]];
  return result;
}

Drag options to blanks, or click blank then click option'

As[length]

Bs[s.length]

Cs[length - 1]

Ds[s.length - 1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using s[s.length] causes undefined access.

Using s[length - 1] is incorrect because length is not a variable.

Add the value of the last character in the string using s[s.length - 1].

Practice

1. What is the main rule to convert Roman numerals to integers?

easy

A. Subtract all values from the largest symbol

B. Add values of symbols, subtract if a smaller symbol is before a larger one

C. Add values only if symbols are the same

D. Multiply values of symbols in order

Solution

1. Step 1: Understand Roman numeral rules

   Roman numerals are added normally, but if a smaller numeral appears before a larger one, it is subtracted.

2. Step 2: Apply addition and subtraction rules

   For example, IV is 5 - 1 = 4, while VI is 5 + 1 = 6.

3. Final Answer:

   Add values of symbols, subtract if a smaller symbol is before a larger one -> Option B

4. Quick Check:

   Roman numeral rules = Add and subtract [OK]

Hint: Subtract when smaller numeral precedes larger one [OK]

Common Mistakes:

• Always adding without subtraction
• Multiplying values incorrectly
• Ignoring order of symbols

2. Which of the following is the correct JavaScript syntax to get the integer value of a Roman numeral character from a map object named romanMap?

easy

A. romanMap['V']

B. romanMap.get('V')

C. romanMap.V

D. romanMap('V')

Solution

1. Step 1: Identify the data structure type

   If romanMap is a plain JavaScript object, access values using square brackets with the key as a string.

2. Step 2: Choose correct syntax for object property access

   Using romanMap['V'] correctly accesses the value for key 'V'. romanMap.get('V') is for Map objects, not plain objects.

3. Final Answer:

   romanMap['V'] -> Option A

4. Quick Check:

   Object property access = romanMap['V'] [OK]

Hint: Use square brackets for object keys as strings [OK]

Common Mistakes:

• Using .get() on plain objects
• Using dot notation with string keys
• Calling object like a function

3. What will be the output of the following JavaScript code?

function romanToInt(s) {
  const map = {I:1, V:5, X:10, L:50, C:100, D:500, M:1000};
  let total = 0;
  for(let i = 0; i < s.length; i++) {
    const current = map[s[i]];
    const next = map[s[i+1]] || 0;
    if(current < next) {
      total -= current;
    } else {
      total += current;
    }
  }
  return total;
}
console.log(romanToInt('IX'));

medium

A. 9

B. 11

C. 1

D. Error

Solution

1. Step 1: Trace the loop for input 'IX'

   For 'I' (1), next is 'X' (10), since 1 < 10, subtract 1 (total = -1). For 'X' (10), next is undefined (0), so add 10 (total = 9).

2. Step 2: Calculate final total

   Total after loop is 9, which is the integer value of 'IX'.

3. Final Answer:

   9 -> Option A

4. Quick Check:

   'IX' = 9 [OK]

Hint: Subtract if current < next, else add [OK]

Common Mistakes:

• Adding all values without subtraction
• Ignoring next character check
• Off-by-one errors in loop

4. Find the error in this JavaScript function for Roman to Integer conversion:

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

medium

A. Use '==' instead of '<' in if condition

B. map object keys should be lowercase

C. total should be initialized to 1

D. Loop condition should be i < s.length, not i <= s.length

Solution

1. Step 1: Analyze loop boundary

   The loop runs from i = 0 to i <= s.length, which means it accesses s[s.length], an undefined index causing current to be undefined.

2. Step 2: Correct loop condition

   Changing loop condition to i < s.length prevents accessing out-of-bound index and avoids errors.

3. Final Answer:

   Loop condition should be i < s.length, not i <= s.length -> Option D

4. Quick Check:

   Loop boundary off-by-one error fixed [OK]

Hint: Use i < length to avoid out-of-bound errors [OK]

Common Mistakes:

• Using <= instead of < in loops
• Wrong case for map keys
• Incorrect comparison operators

5. Given the Roman numeral string 'MCMXCIV', what integer should the conversion function return?

hard

A. 2004

B. 1904

C. 1994

D. 1094

Solution

1. Step 1: Break down the Roman numeral 'MCMXCIV'

   M = 1000, CM = 900 (1000 - 100), XC = 90 (100 - 10), IV = 4 (5 - 1).

2. Step 2: Add all parts

   1000 + 900 + 90 + 4 = 1994 total.

3. Final Answer:

   1994 -> Option C

4. Quick Check:

   'MCMXCIV' = 1994 [OK]

Hint: Identify subtractive pairs and sum all values [OK]

Common Mistakes:

• Adding all numerals without subtraction
• Misreading subtractive pairs
• Confusing similar numerals