This tutorial will show you how to solve HackerRank Valid Username Checker using Kotlin. In different web applications we define certain rules for choosing the username, such as, it should consists of maximum 30 characters; it should not have any special character; it may contain one or more digits; it must starts with a letter, etc. So here also we have some certain rules for choosing the username and we will check valid username regular expression in Kotlin language.

Please read here how to create Kotlin project in Eclipse.

You are updating the username policy on your company’s internal networking platform. According to the policy, a username is considered valid if all the following constraints are satisfied:

The username consists of 8 to 30 characters inclusive. If the username consists of less than 8 or greater than 30 characters, then it is an invalid username.

The username can only contain alphanumeric characters and underscores (_). Alphanumeric characters describe the character set consisting of lowercase characters [a-z], uppercase characters [A-Z], and digits [0-9].

The first character of the username must be an alphabetic character, i.e., either lowercase character [a-z] or uppercase character [A-Z].

For each of the usernames, the code prints true if the username is valid; otherwise false each on a new line.

Sample Input

Julia
Samantha
Samantha_21
1Samantha
Samantha?10_2A
JuliaZ007
Julia@007
_Julia007

Sample Output

false
true
true
false
false
true
false
false

The source code

class ValidUsername {
	companion object {
		@JvmStatic val USER_NAME_REGEX = "^[A-Za-z][A-Za-z0-9_]{7,29}$"
		fun isValidUsername(userName: String): Boolean {
			return USER_NAME_REGEX.toRegex().matches(userName);
		}
	}
}

fun main(args: Array<String>) {
	println(ValidUsername.isValidUsername("Julia"));
	println(ValidUsername.isValidUsername("Samantha"));
	println(ValidUsername.isValidUsername("Samantha_21"));
	println(ValidUsername.isValidUsername("1Samantha"));
	println(ValidUsername.isValidUsername("Samantha?10_2A"));
	println(ValidUsername.isValidUsername("JuliaZ007"));
	println(ValidUsername.isValidUsername("Julia@007"));
	println(ValidUsername.isValidUsername("_Julia007"));
}

Running the Kotlin program

Do right click on the above Kotlin class and select Run As -> Kotlin Application

Output

false
true
true
false
false
true
false
false

Thanks for reading.

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