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Roman to Integer

Steilla Mitchel11912-Jun-2024

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I1
V5
X10
L50
C100
D500
M1000

For example, 2 is written as II in Roman numerals, just two ones are added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written from largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

  • I can be placed before V (5) and X (10) to make 4 and 9. 
  • X can be placed before L (50) and C (100) to make 40 and 90. 
  • C can be placed before D (500) and M (1000) to make 400 and 900.

Given a Roman numeral, convert it to an integer.

c#c# programming language 
Updated on 14-Jun-2024
Steilla Mitchel

Steilla Mitchel

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1 Answers

Ashutosh Kumar Verma

Ashutosh Kumar Verma

14-Jun-2024

Roman to Integer Converter

Here is a simple example to convert the Roman number into an Integer,

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        //take input roman from user to convert into integer
        Console.WriteLine("Enter a roman number to convert into integer");        
        string romanNumeral = Console.ReadLine();

        //convert the input value into uppercase if in lowercase and pass it as an argument to function RomanToInt() 
        int integerValue = RomanToInt(romanNumeral.ToUpper());
        Console.WriteLine("The integer value of the Roman numeral '{0}' is: {1}", romanNumeral, integerValue);

        Console.ReadLine();
    }

    public static int RomanToInt(string s)
    {
        // dictionary for each Roman value with its integer value in key-value format
        Dictionary<char, int> romanToValue = new Dictionary<char, int>()
        {
            {'I', 1},
            {'V', 5},
            {'X', 10},
            {'L', 50},
            {'C', 100},
            {'D', 500},
            {'M', 1000}
        };

        int total = 0;
        int prevValue = 0;

        // iterate over entered input value 
        foreach (char c in s)
        {
            //take the integer value of each Roman value from the dictionary
            int value = romanToValue[c];

            if (value > prevValue)
            {
                total += value - 2 * prevValue;
            }
            else
            {
                total += value;
            }

            prevValue = value;
        }

        return total;
    }
}

In the above example- 

Dictionary- We create a romanToValue dictionary that maps Roman numeric characters to their corresponding integer values.

Variables- We initialize total to 0 to store the last one and prevValue 0 to check the value of the previous number in iteration.

Iteration- Iterate over each character of the input string s.

Logic-
For each character, we get its value from the dictionary.

If the current value is greater than the previous value, it indicates an omitted combination (such as IV or IX). In this case, we add the current value and subtract twice the previous value (because we added it once before).

Otherwise, we will simply add the current value to the total.

We update the prevValue to the current value for the next iteration.

Output-

1. Enter a roman number to convert into integer
XIX
The integer value of the Roman numeral 'XIX' is: 19
-----------------------------------------------------------
2. Enter a roman number to convert into integer
MX
The integer value of the Roman numeral 'MX' is: 1010

 

Also, Read: Prime Number Checker

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