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Leetcode 831. Masking Personal Information

Problem Statement

You are given a string S which can be an email address or a phone number. Your task is to mask the personal information following these rules:

1. Email:

• An email address starts with a name, which can contain letters, digits, dots (‘.’), and underscores (‘_’).
• This is followed by the ‘@’ symbol and then a domain name which is always a lowercase word followed by a period and another lowercase word.
• You need to mask all characters in the name except the first and last character. The masked email must be in form: first_character*****last_character@domain.

2. Phone Number:

• A phone number contains 10 to 13 digits and can contain spaces, dashes (‘-‘), plus (‘+’), and parenthesis (‘(‘ and ‘)’).
• You need to mask all digits except the last 4. The masked phone number must be in the form ***-***-XXXX, where XXXX are the last four digits.
• In addition, if the nation code is present (i.e., more than 10 digits), it must be preceded by a ‘+’ symbol and masked according to the number of digits: e.g., for 12 digits it would be +**.

Given the string S, you need to return the masked version of either the email or the phone number.

Clarifying Questions

1. Can input string S be assumed to be well-formatted?
2. Is it possible for the input string to be neither an email nor a phone number?
3. Shall we expect valid email (not malformed)?
4. Do phone numbers always have digits at the right positions (last 10 to 13 characters)?
5. Are there any constraints on the character case for email?

Strategy

1. Recognize Email or Phone Number:

• Check for the presence of the ‘@’ character to identify an email.
• Otherwise, treat the string as a phone number.

2. Masking the Email:

• Split the email into the name and the domain.
• Only mask the characters between the first and last characters of the name part.

3. Masking the Phone Number:

• Retain only digits and determine the number of digits.
• Reveal the last four digits and appropriately prefix the national code if present.

4. Regex patterns and standard library methods will aid in recognizing and transforming the string accordingly.

Code

public class Solution {
    public String maskPII(String S) {
        if (S.contains("@")) {
            return maskEmail(S);
        } else {
            return maskPhone(S);
        }
    }

    private String maskEmail(String email) {
        email = email.toLowerCase();
        String[] parts = email.split("@");
        String namePart = parts[0];
        String domainPart = parts[1];
        return namePart.charAt(0) + "*****" + namePart.charAt(namePart.length() - 1) + "@" + domainPart;
    }

    private String maskPhone(String phone) {
        StringBuilder digits = new StringBuilder();
        for (char c : phone.toCharArray()) {
            if (Character.isDigit(c)) {
                digits.append(c);
            }
        }

        int len = digits.length();
        String localNumber = "***-***-" + digits.substring(len - 4);
        if (len == 10) {
            return localNumber;
        } else {
            StringBuilder maskedPhone = new StringBuilder("+");
            for (int i = 0; i < len - 10; i++) {
                maskedPhone.append('*');
            }
            maskedPhone.append('-').append(localNumber);
            return maskedPhone.toString();
        }
    }

    // Test the functionality
    public static void main(String[] args) {
        Solution sol = new Solution();
        System.out.println(sol.maskPII("LeetCode@LeetCode.com")); // Expected: "l*****e@leetcode.com"
        System.out.println(sol.maskPII("AB@qq.com"));             // Expected: "a*****b@qq.com"
        System.out.println(sol.maskPII("1(234)567-890"));          // Expected: "***-***-7890"
        System.out.println(sol.maskPII("+123-456-789-0123"));     // Expected: "+**-***-***-0123"
    }
}

Time Complexity

• Email Masking: O(n) due to string manipulations and split operations where n is the length of the input string.
• Phone Masking: O(n) for iterating through the string to extract digits and then constructing the masked phone number where n is the length of the input string.

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