Validating Roman Numerals Using Regular expression

Last Updated : 27 Jan, 2023

Given a String, and You have to validate whether the given String is Valid Roman Numeral or not. If it is valid print True else False.
Note: Numerals are lying between 1 to 3999.
Examples:

Input: String = IX  
Output: True 

Input: String = 54IVC 
Output: False

Roman numerals are based on below symbols.

SYMBOL       VALUE
I             1
IV            4
V             5
IX            9
X             10
XL            40
L             50
XC            90
C             100
CD            400
D             500
CM            900 
M             1000

A number in Roman Numerals is a string of these symbols written in descending order(e.g. M’s first, followed by D’s, etc.). However, in a few specific cases, to avoid four characters being repeated in succession (such as IIII or XXXX), subtractive notation is often used as follows:

I placed before V or X indicates one less, so four is IV (one less than 5) and 9 is IX (one less than 10).
X placed before L or C indicates ten less, so forty is XL (10 less than 50) and 90 is XC (ten less than a hundred).
C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand).

Approach:

The Regular Expression to check if a string is Valid Roman Numeral or not is this:

 ^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$

In which,
1. M{0,3} specifies the thousands section and basically restrains it to between 0 and 4000
2. (CM|CD|D?C{0,3}) is for the hundreds section.
3. (XC|XL|L?X{0,3}) is for the tens place.
4. Finally, (IX|IV|V?I{0,3}) is the units section.
Import regular expression and search the input string in the expression if the string exists return True else return False

Below is the implementation of the above approach.

C++

// C++ program to validate the
//  Roman numeral
 
#include <iostream>
#include <regex>
using namespace std;
 
// Function to validate the
// Roman numeral
bool ValidationOfRomanNumerals(string str)
{
 
    // Regex to check valid
    // ROMAN NUMERAL .
    const regex pattern("^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$");
 
    // If the str
    // is empty return false
    if (str.empty()) {
        return false;
    }
 
    // Return true if the str
    // matched the ReGex
    if (regex_match(str, pattern)) {
        return true;
    }
    else {
        return false;
    }
}
 
// Driver Code
int main()
{
   
    // Test Case 1:
    string str1 = "IX";
    cout << ValidationOfRomanNumerals(str1) << endl;
 
    return 0;
}
 
// This code is contributed by rahulchauhan2020model.

Java

// Java program to validate the
// the Roman numeral
import java.util.regex.*;
 
class GFG {
 
  // Function to Validate the Roman numeral
  public static boolean
    ValidationOfRomanNumerals(String str)
  {
 
    // Regex to check Roman numeral
    String regex
      = "^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$";
 
    // Compile the ReGex
    Pattern p = Pattern.compile(regex);
 
    // If the str
    // is empty return false
    if (str == null) {
      return false;
    }
 
    // Pattern class contains matcher() method
    // to find matching between given
    // ROMAN NUMERAL regular expression.
    Matcher m = p.matcher(str);
 
    // Return if the str
    // matched the ReGex
    return m.matches();
  }
 
  // Driver Code.
  public static void main(String args[])
  {
 
    // Test Case 1:
    String str1 = "IX";
    System.out.println(
      "IS " + str1 + " valid ROMAN NUMERAL:? "
      + ValidationOfRomanNumerals(str1));
  }
}
 
// This code is contributed by rahulchauhan2020model.

Python3

# Python3 program to Validate the Roman numeral
 
# Function to Validate the Roman numeral
def ValidationOfRomanNumerals(string):
     
    # Importing regular expression
    import re
     
    # Searching the input string in expression and 
    # returning the boolean value
    print(bool(re.search(r"^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$",string)))
 
# Driver code
 
# Given string
string="XI"
 
# Function call
ValidationOfRomanNumerals(string)

C#

// C# program to validate
// the Roman numeral using Regular Expression
using System;
using System.Text.RegularExpressions;
class GFG
{
 
  // Main Method
  static void Main(string[] args)
  {
 
    // Input strings to Match
    //the Roman numeral
  
    string[] str={"IX"};
    foreach(string s in str) {
      Console.WriteLine( ValidationOfRomanNumerals(s) ? "true" : "false"); 
    }
    Console.ReadKey(); }
 
  // method containing the regex
  public static bool ValidationOfRomanNumerals(string str)
  {
    string strRegex = @"^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$";
    Regex re = new Regex(strRegex);
    if (re.IsMatch(str))
      return (true);
    else
      return (false);
  }
}
 
// This code is contributed by Rahul Chauhan

Javascript

// Javascript program to validate
// ROMAN NUMERAL using Regular Expression
 
// Function to validate the
// ROMAN NUMERAL
function ValidationOfRomanNumerals(str)
{
 
    // Regex to check valid
    // ROMAN NUMERAL
    let regex = new RegExp(/^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$/);
 
    // str
    // is empty return false
    if (str == null) {
        return "false";
    }
 
    // Return true if the str
    // matched the ReGex
    if (regex.test(str) == true) {
        return "true";
    }
    else {
        return "false";
    }
}
 
// Driver Code
// Test Case 1:
let str1 = "XI";
console.log(ValidationOfRomanNumerals(str1));
 
// This code is contributed by rahulchauhan2020model.