Roman to Integer Conversion in DSA Python - Build from Scratch

Roman to Integer Conversion

📖 Scenario: Imagine you are building a simple tool that helps convert Roman numerals into regular numbers. This is useful in many places like reading old clocks, books, or historical dates.

🎯 Goal: You will create a program that takes a Roman numeral string and converts it into its integer value.

📋 What You'll Learn

Create a dictionary mapping Roman numeral characters to their integer values.

Create a variable to hold the total integer value.

Use a loop to process each character in the Roman numeral string.

Handle the subtraction rule where a smaller numeral before a larger numeral means subtraction.

Print the final integer value.

💡 Why This Matters

🌍 Real World

Roman numerals are used in clocks, book chapters, movie sequels, and historical dates. Converting them to integers helps computers understand and work with these numbers.

💼 Career

Understanding how to map symbols to values and apply rules is key in programming tasks like parsing, data conversion, and working with custom formats.

1

Create Roman numeral dictionary

Create a dictionary called roman_values with these exact entries: 'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000.

DSA Python

# Your code here

Hint

Use curly braces {} to create a dictionary and add the given key-value pairs.

2

Set up input and total variable

Create a variable called roman and set it to the string 'MCMXCIV'. Then create a variable called total and set it to 0.

DSA Python

roman_values = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
# Your code here

Hint

Assign the string 'MCMXCIV' to roman and number 0 to total.

3

Convert Roman numeral to integer

Use a for loop with variable i to iterate over the range from 0 to len(roman) - 1. Inside the loop, compare the value of the current Roman numeral character roman[i] with the next character roman[i + 1] using roman_values. If the current value is less than the next value, subtract it from total. Otherwise, add it to total. After the loop, add the value of the last character roman[-1] to total.

DSA Python

roman_values = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
roman = 'MCMXCIV'
total = 0
# Your code here

Hint

Use range(len(roman) - 1) to loop through all but the last character. Compare current and next values to decide whether to add or subtract.

4

Print the integer result

Write print(total) to display the final integer value of the Roman numeral.

DSA Python

roman_values = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
roman = 'MCMXCIV'
total = 0
for i in range(len(roman) - 1):
    if roman_values[roman[i]] < roman_values[roman[i + 1]]:
        total -= roman_values[roman[i]]
    else:
        total += roman_values[roman[i]]
total += roman_values[roman[-1]]
# Your code here

Hint

Use the print function to show the value stored in total.