# Match flight number using Regular Expression

• Last Updated : 20 Dec, 2022

Given some Flight Numbers, the task is to check if they are valid or not using regular expressions. Rules for the valid flight numbers are:

• It is an alphanumeric string containing uppercase Alphabet letters(A-Z) and digits(0-9).
• It should always start with one of the alphabet letters and should end with always a digit.
• Its length may vary from 5 to 6 characters.
• If it contains whitespaces then by including this whitespace Its length should be between  6 to 7.
• It should not contain any special symbols.

Examples:

Input: str = “A12345”
Output: False
Explanation: First two characters should be from uppercase alphabet letters.

Input: str = “AI123456”
Output: False
Explanation: Its length is 8.

Input: str=”AI 123″
Output: True
Explanation: It follows the above noted points.

Approach: The problem can be solved based on the following idea:

Create a regex pattern to validate the number as written below:
regex= “^[A-Z]{2}\s{0, 1}[0-9]{3, 4}\$”

Where,
^ : Start of the string
[A-Z]{2} :  This pattern will match two of the preceding items in the range from “A” to “Z”.
\s{0, 1} : This pattern will match zero or one the preceding item if It  is a whitespace.
[0-9]{3, 4} : This pattern will match 3 or 4 of the preceding items, if it is in the range from 0 to 9.
\$: End of the String.

Follow the below steps to implement the idea:

• Create a regex expression for flight numbers.
• Use Pattern class to compile the regex formed.
• Use the matcher function to check whether the Flight Number is valid or not.
• If it is valid, return true. Otherwise, return false.

Below is the implementation of the above approach:

## C++

// C++ program to validate the
// Flight Number using Regular
// Expression

#include <bits/stdc++.h>
#include <regex>
using namespace std;

// Function to validate the
// Flight Number
string isValid_FlightNumber(string str)
{
// Regex to check valid
// Flight Number .
const regex pattern("^[A-Z]{2}\\s{0,1}[0-9]{3,4}\$");

// 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 = "AI 123";
cout << isValid_FlightNumber(str1) << endl;

// Test Case 2:
string str2 = "AI 1234";
cout << isValid_FlightNumber(str2) << endl;

// Test Case 3:
string str3 = "AI1234";
cout << isValid_FlightNumber(str3) << endl;

// Test Case 4:
string str4 = "AI 12AA";
cout << isValid_FlightNumber(str4) << endl;

// Test Case 5:
string str5 = "AI123456";
cout << isValid_FlightNumber(str5) << endl;

// Test Case 6:
string str6 = "A12345";
cout << isValid_FlightNumber(str6) << endl;

return 0;
}

## Java

// Java program to validate the
// Flight Number using Regular Expression

import java.util.regex.*;

class GFG {

// Function to validate the
// Flight Number
public static boolean isValid_FlightNumber(String str)
{
// Regex to check valid Flight Number
String regex = "^[A-Z]{2}\\s{0, 1}[0-9]{3, 4}\$";

// 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 str using regex.
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 = "AI 123";
System.out.println(isValid_FlightNumber(str1));

// Test Case 2:
String str2 = "AI 1234";
System.out.println(isValid_FlightNumber(str2));

// Test Case 3:
String str3 = "AI1234";
System.out.println(isValid_FlightNumber(str3));

// Test Case 4:
String str4 = "AI 12AA";
System.out.println(isValid_FlightNumber(str4));

// Test Case 5:
String str5 = "AI123456";
System.out.println(isValid_FlightNumber(str5));

// Test Case 6:
String str6 = "A12345";
System.out.println(isValid_FlightNumber(str6));
}
}

## Python3

# Python3 program to validate
# Flight Number using Regular Expression

import re

# Function to validate
# Flight Number
def isValid_FlightNumber(str):

# Regex to check valid Flight Number
regex = "^[A-Z]{2}\s{0, 1}[0-9]{3, 4}\$"

# 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
if __name__ == '__main__':

# Test Case 1:
str1 = "AI 123"
print(isValid_FlightNumber(str1))

# Test Case 2:
str2 = "AI 1234"
print(isValid_FlightNumber(str2))

# Test Case 3:
str3 = "AI1234"
print(isValid_FlightNumber(str3))

# Test Case 4:
str4 = "AI 12AA"
print(isValid_FlightNumber(str4))

# Test Case 5:
str5 = "AI123456"
print(isValid_FlightNumber(str5))

# Test Case 6:
str6 = "A12345"
print(isValid_FlightNumber(str6))

## C#

// Include namespace system
using System;
using System.Text.RegularExpressions;

public class GFG
{

// Function to validate the
// Flight Number
public static bool isValid_FlightNumber(String str)
{

// Regex to check valid Flight Number
var regex = new Regex("^[A-Z]{2}\\s{0, 1}[0-9]{3, 4}\$");

// If the str
// is empty return false
if (str == null)
{
return false;
}
// Pattern class contains matcher()
// method to find matching between
// given str using regex.
var m = regex.Match(str);
// Return if the str
// matched the ReGex
return m.Success;
}
// Driver Code.
public static void Main(String[] args)
{
// Test Case 1:
var str1 = "AI 123";
Console.WriteLine(GFG.isValid_FlightNumber(str1));

// Test Case 2:
var str2 = "AI 1234";
Console.WriteLine(GFG.isValid_FlightNumber(str2));

// Test Case 3:
var str3 = "AI1234";
Console.WriteLine(GFG.isValid_FlightNumber(str3));

// Test Case 4:
var str4 = "AI 12AA";
Console.WriteLine(GFG.isValid_FlightNumber(str4));

// Test Case 5:
var str5 = "AI123456";
Console.WriteLine(GFG.isValid_FlightNumber(str5));

// Test Case 6:
var str6 = "A12345";
Console.WriteLine(GFG.isValid_FlightNumber(str6));
}
}

// This code is contributed by aadityaburujwale.

## Javascript

// Javascript program to validate
// flight Number using Regular Expression

// Function to validate the
// Flight Number
function isValid_FlightNumber(str) {
// Regex to check valid
// Flight Number
let regex = new RegExp(/^[A-Z]{2}\s{0, 1}[0-9]{3, 4}\$/);

// If 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 = "AI 123";
console.log(isValid_FlightNumber(str1));

// Test Case 2:
let str2 = "AI 1234";
console.log(isValid_FlightNumber(str2));

// Test Case 3:
let str3 = "AI1234";
console.log(isValid_FlightNumber(str3));

// Test Case 4:
let str4 = "AI 12AA";
console.log(isValid_FlightNumber(str4));

// Test Case 5:
let str5 = "AI123456";
console.log(isValid_FlightNumber(str5));

// Test Case 6:
let str6 = "A12345";
console.log(isValid_FlightNumber(str6));

Output

false
false
false
false
false
false

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

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