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# US currency validation using Regular Expressions

Given some  US Currencies, the task is to check if they are valid or not using regular expressions. Rules for the valid Currency are:

• It can contain only digits (0 – 9) and at most one dot.
• It should not contain any whitespaces and alphabets.
• Comma Separator (‘, ‘) should be there after every three digits interval.

Examples:

Input: “\$0.84”
Output: True

Input: “12345”
Output: False
Explanation: “\$” is missing in the starting.

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

Create a regex pattern to validate the number as written below:
regex = ^\\$([0-9]{1, 3}(\, [0-9]{3})*|([0-9]+))(\.[0-9]{2})?\$”

OR

regex=”^\\$(\d{1, 3}(\, \d{3})*|(\d+))(\.\d{2})?\$

Where,

• ^ : Represents, beginning of the string
• \\$ : Should always start from \$
• \d : Digits should be there
• \. : dot can be present or not
• \d{2} : Only digits are allowed after dot

Follow the below steps to implement the idea:

• Create a regex expression for US Currency.
• Use Pattern class to compile the regex formed.
• Use the matcher function to check whether the US Currency 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
// US CURRENCY using Regular
// Expression

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

// Function to validate the
// US CURRENCY
string isValid_USCurrency(string str)
{
// Regex to check valid
// US CURRENCY.
const regex pattern(
"^\\\$(\\d{1, 3}(\\, \\d{3})*|(\\d+))(\\.\\d{2})?\$");

// 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 = "\$123458";
cout << isValid_USCurrency(str1) << endl;

// Test Case 2:
string str2 = "\$1, 234, 567.89";
cout << isValid_USCurrency(str2) << endl;

// Test Case 3:
string str3 = "\$0.84";
cout << isValid_USCurrency(str3) << endl;

// Test Case 4:
string str4 = "\$12, 3456.01";
cout << isValid_USCurrency(str4) << endl;

// Test Case 5:
string str5 = "\$1.234";
cout << isValid_USCurrency(str5) << endl;

return 0;
}```

## Java

```// Java program to validate the
// US Currency using Regular Expression

import java.util.regex.*;

class GFG {

// Function to validate the
// US Currency
public static boolean isValid_USCurrency(String str)
{
// Regex to check valid  US Currency
String regex
= "^\\\$(\\d{1, 3}(\\, \\d{3})*|(\\d+))(\\.\\d{2})?\$";

// 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 = "\$123458";
System.out.println(isValid_USCurrency(str1));

// Test Case 2:
String str2 = "\$1, 234, 567.89";
System.out.println(isValid_USCurrency(str2));

// Test Case 3:
String str3 = "\$0.84";
System.out.println(isValid_USCurrency(str3));

// Test Case 4:
String str4 = "\$12, 3456.01";
System.out.println(isValid_USCurrency(str4));

// Test Case 5:
String str5 = "\$1.234";
System.out.println(isValid_USCurrency(str5));
}
}```

## Python3

```# Python3 program to validate
# US Currency using Regular Expression

import re

# Function to validate
# US Currency
def isValid_USCurrency(str):

# Regex to check valid US Currency
regex = "^\\\$(\\d{1, 3}(\\, \\d{3})*|(\\d+))(\\.\\d{2})?\$"

# 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 = "\$123458"
print(isValid_USCurrency(str1))

# Test Case 2:
str2 = "\$1, 234, 567.89"
print(isValid_USCurrency(str2))

# Test Case 3:
str3 = "\$0.84"
print(isValid_USCurrency(str3))

# Test Case 4:
str4 = "\$12, 3456.01"
print(isValid_USCurrency(str4))

# Test Case 5:
str5 = "\$1.234"
print(isValid_USCurrency(str5))
```

## C#

```// C# program to validate the
// US Currency using Regular Expression
using System;
using System.Text.RegularExpressions;

public class GFG {

// Function to validate the
// US Currency
public static bool isValid_USCurrency(string str)
{
// Regex to check valid US Currency
string regex
= "^\\\$(\\d{1, 3}(\\, \\d{3})*|(\\d+))(\\.\\d{2})?\$";

// Compile the ReGex
Regex p = new Regex(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.
Match m = p.Match(str);

// Return if the str
// matched the ReGex
return m.Success;
}

// Driver Code.
public static void Main()
{
// Test Case 1:
string str1 = "\$123458";
Console.WriteLine(isValid_USCurrency(str1));

// Test Case 2:
string str2 = "\$1, 234, 567.89";
Console.WriteLine(isValid_USCurrency(str2));

// Test Case 3:
string str3 = "\$0.84";
Console.WriteLine(isValid_USCurrency(str3));

// Test Case 4:
string str4 = "\$12, 3456.01";
Console.WriteLine(isValid_USCurrency(str4));

// Test Case 5:
string str5 = "\$1.234";
Console.WriteLine(isValid_USCurrency(str5));
}
}

// This code is contributed by Pushpesh Raj.```

## Javascript

```// Javascript program to validate
// US Currency using Regular Expression

// Function to validate the
// US Currency
function isValid_USCurrency(str) {
// Regex to check valid
// US Currency
let regex = new RegExp(/^\\$(\d{1, 3}(\, \d{3})*|(\d+))(\.\d{2})?\$/);

// 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 = "\$123458";
console.log(isValid_USCurrency(str1));

// Test Case 2:
let str2 = "\$1, 234, 567.89";
console.log(isValid_USCurrency(str2));

// Test Case 3:
let str3 = "\$0.84";
console.log(isValid_USCurrency(str3));

// Test Case 4:
let str4 = "\$12, 3456.01";
console.log(isValid_USCurrency(str4));

// Test Case 5:
let str5 = "\$1.234";
console.log(isValid_USCurrency(str5));```
Output

```true
true
true
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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