Roman to Integer Conversion in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the result variable to zero.

DSA Typescript

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

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

Aundefined

B0

C1

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing result with 1 or null causes wrong calculations.

Leaving result undefined leads to errors.

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

2fill in blank

medium

Complete the code to get the integer value of a Roman numeral character from the map.

DSA Typescript

const romanMap: { [key: string]: number } = {I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000};

function romanToInt(s: string): number {
  let result = 0;
  for (let i = 0; i < s.length; i++) {
    let current = romanMap[[1]];
  }
  return result;
}

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

As[i]

Bi

Cs

DromanMap[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using i instead of s[i] causes wrong key lookup.

Using romanMap[i] is incorrect because i is a number index.

We use s[i] to get the current Roman numeral character at index i.

3fill in blank

hard

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

DSA Typescript

for (let i = 0; i < s.length - 1; i++) {
  let current = romanMap[s[i]];
  let next = romanMap[s[i + 1]];
  if (current [1] next) {
    result -= current;
  } else {
    result += current;
  }
}

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 handle subtraction correctly.

If current is less than next, we subtract current from result.

4fill in blank

hard

Fill both blanks to add the last Roman numeral value after the loop and return the result.

DSA Typescript

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 [1] romanMap[s[s.length [2] 1]];
return result;

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

A+=

B-=

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' subtracts the last value incorrectly.

Using '+' instead of '- 1' causes index out of range.

We add the value of the last Roman numeral to result using '+=' and access it with s.length - 1.

5fill in blank

hard

Fill all three blanks to complete the function that converts a Roman numeral string to an integer.

DSA Typescript

function romanToInt(s: string): number {
  const romanMap: { [key: string]: number } = {I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000};
  let result = [1];
  for (let i = 0; i < s.length - 1; i++) {
    let current = romanMap[s[i]];
    let next = romanMap[s[i + 1]];
    if (current [2] next) {
      result -= current;
    } else {
      result += current;
    }
  }
  result [3] romanMap[s[s.length - 1]];
  return result;
}

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

A0

B<

C+=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting result at 1 causes off-by-one errors.

Using '>' instead of '<' reverses subtraction logic.

Forgetting to add the last numeral causes wrong totals.

Initialize result to 0, subtract when current < next, and add the last value with '+='.

Practice

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

easy

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

B. Multiply all symbol values together

C. Add values only if symbols are the same

D. Subtract all symbol values from 1000

Solution

1. Step 1: Understand Roman numeral rules

   Roman numerals are converted by adding values of symbols, but if a smaller value comes before a larger one, it is subtracted.

2. Step 2: Apply the rule to conversion

   For example, IV is 5 - 1 = 4, not 1 + 5 = 6.

3. Final Answer:

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

4. Quick Check:

   Roman to integer = add/subtract values [OK]

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

Common Mistakes:

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

2. Which TypeScript syntax correctly defines a function to convert Roman numerals to integers?

easy

A. def romanToInt(s): return 0

B. function romanToInt(s: string): number { return 0; }

C. func romanToInt(s string) int { return 0 }

D. romanToInt = (s) => { return '0'; }

Solution

1. Step 1: Identify TypeScript function syntax

   TypeScript functions use the syntax: function name(params): returnType { body }

2. Step 2: Match correct syntax

   function romanToInt(s: string): number { return 0; } matches TypeScript syntax with parameter type and return type specified.

3. Final Answer:

   function romanToInt(s: string): number { return 0; } -> Option B

4. Quick Check:

   TypeScript function syntax = function romanToInt(s: string): number { return 0; } [OK]

Hint: Use 'function name(params: type): returnType' in TypeScript [OK]

Common Mistakes:

• Using Python or Go syntax in TypeScript
• Returning string instead of number
• Missing type annotations

3. What is the output of this TypeScript code?

function romanToInt(s: string): number {
  const map: {[key: string]: number} = {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. 11

B. 4

C. 9

D. Error

Solution

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

   For 'I' (1) and next 'X' (10), since 1 < 10, subtract 1. For 'X' (10), no next, add 10.

2. Step 2: Calculate total

   Total = -1 + 10 = 9.

3. Final Answer:

   9 -> Option C

4. Quick Check:

   'IX' = 9 [OK]

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

Common Mistakes:

• Adding all values without subtraction
• Off-by-one error in loop
• Not handling last character correctly

4. Find the bug in this TypeScript code for Roman to Integer conversion:

function romanToInt(s: string): number {
  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. Return type should be string, not number

B. map object keys should be lowercase

C. Use 'var' instead of 'let' for i

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

Solution

1. Step 1: Check loop boundary

   The loop runs from i = 0 to i <= s.length, which causes s[i] to be undefined at last iteration.

2. Step 2: Correct loop condition

   Change to i < s.length to avoid accessing undefined index.

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-bounds access [OK]

Common Mistakes:

• Using <= instead of < in loops
• Wrong case for map keys
• Incorrect return type

5. Given the Roman numeral string 'MCMXCIV', what integer does the following TypeScript function return?

function romanToInt(s: string): number {
  const map: {[key: string]: number} = {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('MCMXCIV'));

hard

A. 1994

B. 1904

C. 2004

D. 1494

Solution

1. Step 1: Break down 'MCMXCIV'

   M=1000, C=100, M=1000, X=10, C=100, I=1, V=5. Apply subtraction where smaller precedes larger.

2. Step 2: Calculate total step-by-step

   1000 (M) + (100 < 1000, subtract 100) + 1000 + (10 < 100, subtract 10) + 100 + (1 < 5, subtract 1) + 5 = 1000 - 100 + 1000 - 10 + 100 - 1 + 5 = 1994.

3. Final Answer:

   1994 -> Option A

4. Quick Check:

   'MCMXCIV' = 1994 [OK]

Hint: Subtract smaller before larger, else add [OK]

Common Mistakes:

• Adding all values without subtraction
• Misreading symbol order
• Skipping last character