Hackerrank Valid Username Regular Expression Solution

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  to  characters inclusive. If the username consists of less than  or greater than  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 , uppercase characters , and digits .
• The first character of the username must be an alphabetic character, i.e., either lowercase character  or uppercase character .

Update the value of regularExpression field in the UsernameValidator class so that the regular expression only matches with valid usernames.

Input Format.

The first line of input contains an integer , describing the total number of usernames. Each of the next  lines contains a string describing the username. The locked stub code reads the inputs and validates the username.

Constraints.

• The username consists of any printable characters.

Output Format.

For each of the usernames, the locked stub code prints Valid if the username is valid; otherwise Invalid each on a new line.

Sample Input 0.

8
Julia
Samantha
Samantha_21
1Samantha
Samantha?10_2A
JuliaZ007
Julia@007
_Julia007

Sample Output 0.

Invalid
Valid
Valid
Invalid
Invalid
Valid
Invalid
Invalid

Explanation 0.

Refer diagram in the challenge statement.

Solution in java8#

Approach 1.

class UsernameValidator {
    /*
     * Write regular expression here.
     */
    public static final String regularExpression = "[a-zA-Z](\\w){7,29}";
}

Approach 2.

class UsernameValidator {
    /*
     * Write regular expression here.
     */
    public static final String regularExpression = "^[A-Za-z]\\w{7,29}$";
}

Approach 3.

class UsernameValidator {
    /*
     * Write regular expression here.
     */
    public static final String regularExpression = "\\p{Alpha}(\\w|_){7,29}";
}