How to validate GST (Goods and Services Tax) number using Regular Expression

Given string str, the task is to check whether the given string is a valid GST (Goods and Services Tax) number or not using Regular Expression. 
The valid GST (Goods and Services Tax) number must satisfy the following conditions: 

1. It should be 15 characters long.
2. The first 2 characters should be a number.
3. The next 10 characters should be the PAN number of the taxpayer.
4. The 13th character (entity code) should be a number from 1-9 or an alphabet.
5. The 14th character should be Z.
6. The 15th character should be an alphabet or a number.

Examples:

Input: str = “06BZAHM6385P6Z2”; 
Output: true 
Explanation:
The given string satisfies all the above mentioned conditions. Therefore, it is a valid GST (Goods and Services Tax) number.

Input: str = “06BZAF67”; 
Output: false 
Explanation:
The given string is not 15 characters long. Therefore, it is not a valid GST (Goods and Services Tax) number.

Input: str = “AZBZAHM6385P6Z2”; 
Output: false 
Explanation:
The given string starts with alphabet. Therefore, it is not a valid GST (Goods and Services Tax) number. 

Approach: The idea is to use the concept of Regular Expression to solve this problem. The following steps can be followed to compute the answer: 

• Get the String.
• Create a regular expression to check valid GST (Goods and Services Tax) number as mentioned below:

regex = “^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$”; 

• Where: 
  • ^ represents the starting of the string.
  • [0-9]{2} represents the first two characters should be a number.
  • [A-Z]{5} represents the next five characters should be any upper case alphabets.
  • [0-9]{4} represents the next four characters should be any number.
  • [A-Z]{1} represents the next character should be any upper case alphabet.
  • [1-9A-Z]{1} represents the 13th character should be a number from 1-9 or an alphabet.
  • Z represents the 14th character should be Z.
  • [0-9A-Z]{1} represents the 15th character should be an alphabet or a number.
  • $ represents the ending of the string.
• Match the given string with the Regular Expression. In Java, this can be done by using Pattern.matcher().
• Return true if the string matches with the given regular expression, else return false.

Below is the implementation of the above approach:

C++

// C++ program to validate the
// GST (Goods and Services Tax) number
// using Regular Expression
#include <iostream>
#include <regex>
using namespace std;

// Function to validate the GST
// (Goods and Services Tax) number
bool isValidGSTNo(string str)
{

    // Regex to check valid GST
    // (Goods and Services Tax) number
    const regex pattern("^[0-9]{2}[A-Z]{5}"
                        "[0-9]{4}[A-Z]{1}["
                        "1-9A-Z]{1}Z[0-9A-Z]{1}$");

    // If the GST (Goods and Services Tax)
    // number is empty return false
    if (str.empty())
    {
        return false;
    }

    // Return true if the GST number
    // matched the ReGex
    if (regex_match(str, pattern))
    {
        return true;
    }
    else
    {
        return false;
    }
}

// Driver Code
int main()
{
    // Test Case 1:
    string str1 = "06BZAHM6385P6Z2";
    cout << isValidGSTNo(str1) << endl;

    // Test Case 2:
    string str2 = "06BZAF67";
    cout << isValidGSTNo(str2) << endl;

    // Test Case 3:
    string str3 = "AZBZAHM6385P6Z2";
    cout << isValidGSTNo(str3) << endl;

    // Test Case 4:
    string str4 = "06BZ63AHM85P6Z2";
    cout << isValidGSTNo(str4) << endl;

    // Test Case 5:
    string str5 = "06BZAHM6385P6F2";
    cout << isValidGSTNo(str5) << endl;

    return 0;
}

// This code is contributed by yuvraj_chandra

Java

// Java program to validate the
// GST (Goods and Services Tax) number
// using regular expression.

import java.util.regex.*;

class GFG {

    // Function to validate
    // GST (Goods and Services Tax) number.
    public static boolean isValidGSTNo(String str)
    {
        // Regex to check valid
        // GST (Goods and Services Tax) number
        String regex = "^[0-9]{2}[A-Z]{5}[0-9]{4}"
                       + "[A-Z]{1}[1-9A-Z]{1}"
                       + "Z[0-9A-Z]{1}$";

        // Compile the ReGex
        Pattern p = Pattern.compile(regex);

        // If the string is empty
        // return false
        if (str == null)
        {
            return false;
        }

        // Pattern class contains matcher()
        // method to find the matching
        // between the given string
        // and the regular expression.
        Matcher m = p.matcher(str);

        // Return if the string
        // matched the ReGex
        return m.matches();
    }

    // Driver Code.
    public static void main(String args[])
    {

        // Test Case 1:
        String str1 = "06BZAHM6385P6Z2";
        System.out.println(isValidGSTNo(str1));

        // Test Case 2:
        String str2 = "06BZAF67";
        System.out.println(isValidGSTNo(str2));

        // Test Case 3:
        String str3 = "AZBZAHM6385P6Z2";
        System.out.println(isValidGSTNo(str3));

        // Test Case 4:
        String str4 = "06BZ63AHM85P6Z2";
        System.out.println(isValidGSTNo(str4));

        // Test Case 5:
        String str5 = "06BZAHM6385P6F2";
        System.out.println(isValidGSTNo(str5));
    }
}

Python3

# Python3 program to validate
# GST (Goods and Services Tax) number
# using regular expression
import re

# Function to validate GST
# (Goods and Services Tax) number.
def isValidMasterCardNo(str):

    # Regex to check valid
    # GST (Goods and Services Tax) number
    regex = "^[0-9]{2}[A-Z]{5}[0-9]{4}" +
            "[A-Z]{1}[1-9A-Z]{1}" +
            "Z[0-9A-Z]{1}$"

    # Compile the ReGex
    p = re.compile(regex)

    # If the string is empty
    # return false
    if (str == None):
        return False

    # Return if the string
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False

# Driver code

# Test Case 1:
str1 = "06BZAHM6385P6Z2"
print(isValidMasterCardNo(str1))

# Test Case 2:
str2 = "06BZAF67"
print(isValidMasterCardNo(str2))

# Test Case 3:
str3 = "AZBZAHM6385P6Z2"
print(isValidMasterCardNo(str3))

# Test Case 4:
str4 = "06BZ63AHM85P6Z2"
print(isValidMasterCardNo(str4))

# Test Case 5:
str5 = "06BZAHM6385P6F2"
print(isValidMasterCardNo(str5))

# This code is contributed by avanitrachhadiya2155

C#

// C# program to validate the
// GST (Goods and Services Tax) number
//using Regular Expressions
using System;
using System.Text.RegularExpressions;
class GFG
{

// Main Method
static void Main(string[] args)
{

    // Input strings to Match
    // GST (Goods and Services Tax) number
    string[] str={"06BZAHM6385P6Z2","06BZAF67","AZBZAHM6385P6Z2","06BZ63AHM85P6Z2","06BZAHM6385P6F2"};
    foreach(string s in str) {
    Console.WriteLine( isValidGSTNo(s) ? "true" : "false");
    }
    Console.ReadKey(); }

// method containing the regex
public static bool isValidGSTNo(string str)
{
    string strRegex = @"^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$";
    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 the
// GST (Goods and Services Tax) number
// using Regular Expression
// Function to validate the
// GST Number
function isValidGSTNo(str) {
    // Regex to check valid
    // GST CODE
    let regex = new RegExp(/^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$/);

    // GST CODE
    // is empty return false
    if (str == null) {
        return "false";
    }

    // Return true if the GST_CODE
    // matched the ReGex
    if (regex.test(str) == true) {
        return "true";
    }
    else {
        return "false";
    }
}

// Driver Code
// Test Case 1:
let str1 = "06BZAHM6385P6Z2";
console.log(isValidGSTNo(str1));

// Test Case 2:
let str2 = "06BZAF67";
console.log(isValidGSTNo(str2));

// Test Case 3:
let str3 = "AZBZAHM6385P6Z2";
console.log(isValidGSTNo(str3));

// Test Case 4:
let str4 = "06BZ63AHM85P6Z2";
console.log(isValidGSTNo(str4));

// Test Case 5:
let str5 = "06BZAHM6385P6F2";
console.log(isValidGSTNo(str5));


// This code is contributed by Rahul Chauhan

Output

true
false
false
false
false

Time Complexity: O(N) for each testcase, where N is the length of the given string. 
Auxiliary Space: O(1)