Roman to Integer Conversion in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA C#

int GetValue(char roman) {
    switch (roman) {
        case 'I': return [1];
        case 'V': return 5;
        case 'X': return 10;
        case 'L': return 50;
        case 'C': return 100;
        case 'D': return 500;
        case 'M': return 1000;
        default: return 0;
    }
}

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

A10

B0

C1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 instead of 1 for 'I'.

Confusing 'I' with 'V' or 'X'.

The Roman numeral 'I' represents the integer 1.

2fill in blank

medium

Complete the code to iterate through the Roman numeral string from left to right.

DSA C#

for (int i = 0; i [1] s.Length; i++) {
    // process s[i]
}

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

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' causing index out of range exception.

Using '>' or '>=' which never enter the loop.

The loop should run while i is less than s.Length to avoid out-of-range errors.

3fill in blank

hard

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

DSA C#

if (GetValue(s[i]) [1] GetValue(s[i + 1])) {
    result -= GetValue(s[i]);
} else {
    result += GetValue(s[i]);
}

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

A<

B>=

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' which reverses logic.

Using '==' which misses subtraction cases.

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

4fill in blank

hard

Fill both blanks to correctly handle the last character in the Roman numeral string.

DSA C#

if (i == [1] - 1) {
    result += GetValue(s[[2]]);
}

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

As.Length

Bs.Length - 1

Ci

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using s.Length which is out of range.

Using 0 which is the first character, not last.

The last index is s.Length - 1, so add the value of s at that index.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that maps Roman numerals to integers.

DSA C#

var romanMap = new Dictionary<char, int> {
    {'I', [1],
    {'V', [2],
    {'X', [3]
};

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

A1

B5

C10

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing values like assigning 10 to 'V'.

Using 50 for 'X' which is incorrect.

Roman numerals 'I', 'V', and 'X' correspond to 1, 5, and 10 respectively.

Practice

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

easy

A. Subtract all values from the largest symbol

B. Multiply values of all symbols

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

D. Add values only if symbols are in alphabetical order

Solution

1. Step 1: Understand Roman numeral rules

   Roman numerals add values unless a smaller symbol is before a larger one, then subtract.

2. Step 2: Apply rule to conversion

   When converting, add values normally but subtract when a smaller symbol precedes a larger one.

3. Final Answer:

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

4. Quick Check:

   Roman numeral conversion rule = Add values of symbols, subtract if a smaller symbol is before a larger one [OK]

Hint: Subtract only when smaller symbol is before larger one [OK]

Common Mistakes:

• Multiplying values instead of adding/subtracting
• Ignoring subtraction rule
• Adding all values without checking order

2. Which C# code snippet correctly initializes a dictionary for Roman numeral values?

easy

A. var map = new Dictionary { {'I', 1}, {'V', 5} };

B. var map = new Dictionary { {1, 'I'}, {5, 'V'} };

C. var map = new Dictionary { {'I', 1}, {'V', 5} };

D. var map = new Dictionary { {'I', "1"}, {'V', "5"} };

Solution

1. Step 1: Identify correct dictionary types

   Roman numerals are characters mapped to integer values, so Dictionary is correct.

2. Step 2: Check initialization syntax

   Initialization with curly braces and pairs like {'I', 1} is correct syntax in C#.

3. Final Answer:

   var map = new Dictionary { {'I', 1}, {'V', 5} }; -> Option A

4. Quick Check:

   Dictionary with correct pairs = var map = new Dictionary { {'I', 1}, {'V', 5} }; [OK]

Hint: Use Dictionary for Roman numeral mapping [OK]

Common Mistakes:

• Swapping key and value types
• Using string keys instead of char
• Incorrect initialization syntax

3. What is the output of this C# code snippet?

string s = "IX";
var map = new Dictionary { {'I', 1}, {'V', 5}, {'X', 10} };
int result = 0;
for (int i = 0; i < s.Length; i++) {
  if (i + 1 < s.Length && map[s[i]] < map[s[i + 1]]) {
    result -= map[s[i]];
  } else {
    result += map[s[i]];
  }
}
Console.WriteLine(result);

medium

A. 9

B. 11

C. 6

D. 1

Solution

1. Step 1: Analyze loop and conditions

   For 'IX', at i=0: 'I' < 'X' so subtract 1; at i=1: add 10.

2. Step 2: Calculate result

   result = -1 + 10 = 9.

3. Final Answer:

   9 -> Option A

4. Quick Check:

   IX = 9 [OK]

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

Common Mistakes:

• Adding all values without subtraction
• Off-by-one errors in loop
• Incorrect dictionary values

4. Find the error in this C# code for Roman to integer conversion:

var map = new Dictionary { {'I', 1}, {'V', 5}, {'X', 10} };
int result = 0;
for (int i = 0; i < s.Length - 1; i++) {
  if (map[s[i]] < map[s[i + 1]]) {
    result -= map[s[i]];
  } else {
    result += map[s[i]];
  }
}
result += map[s[s.Length - 1]];
Console.WriteLine(result);

medium

A. No error, code works correctly

B. Missing initialization of string s

C. Loop should run till i < s.Length, not s.Length - 1

D. Dictionary keys should be strings, not chars

Solution

1. Step 1: Check variable declarations

   The variable 's' is used but not declared or initialized, causing a compile error.

2. Step 2: Verify loop and dictionary usage

   Loop and dictionary usage are correct; only 's' is missing.

3. Final Answer:

   Missing initialization of string s -> Option B

4. Quick Check:

   Undefined variable s causes error = Missing initialization of string s [OK]

Hint: Always declare and initialize variables before use [OK]

Common Mistakes:

• Forgetting to declare input string
• Incorrect loop range causing index errors
• Wrong dictionary key types

5. Given the Roman numeral string "MCMXCIV", what integer does the following C# code output?

string s = "MCMXCIV";
var map = new Dictionary {
  {'I', 1}, {'V', 5}, {'X', 10}, {'L', 50}, {'C', 100}, {'D', 500}, {'M', 1000}
};
int result = 0;
for (int i = 0; i < s.Length; i++) {
  if (i + 1 < s.Length && map[s[i]] < map[s[i + 1]]) {
    result -= map[s[i]];
  } else {
    result += map[s[i]];
  }
}
Console.WriteLine(result);

hard

A. 1494

B. 1904

C. 2000

D. 1994

Solution

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

   M=1000, CM=900, XC=90, IV=4; sum = 1000 + 900 + 90 + 4.

2. Step 2: Calculate total value using code logic

   Code subtracts smaller before larger and adds others: 1000 - 100 + 1000 - 10 + 100 - 1 + 5 = 1994.

3. Final Answer:

   1994 -> Option D

4. Quick Check:

   MCMXCIV = 1994 [OK]

Hint: Sum values, subtract when smaller precedes larger [OK]

Common Mistakes:

• Adding all values without subtraction
• Misreading compound numerals like CM or XC
• Incorrect dictionary values