#831

Medium

auto_awesomeString-driven solution strategy

LeetCode Problem Workspace

Masking Personal Information

This problem requires masking sensitive parts of emails and phone numbers using a precise string-driven strategy efficiently.

string

Problem Statement

You are given a string s that contains personal information, either an email address or a phone number. Your task is to return a masked version of this information following specific rules to protect privacy.

For emails, convert all letters to lowercase and replace all characters between the first and last letter of the name with five asterisks. For phone numbers, remove all non-digit characters, identify the local and country code, and mask every digit except the last four with asterisks, preserving formatting as needed.

Examples

Example 1

Input: s = "LeetCode@LeetCode.com"

Output: "l*e@leetcode.com"

s is an email address. The name and domain are converted to lowercase, and the middle of the name is replaced by 5 asterisks.

Example 2

Input: s = "AB@qq.com"

Output: "a*b@qq.com"

s is an email address. The name and domain are converted to lowercase, and the middle of the name is replaced by 5 asterisks. Note that even though "ab" is 2 characters, it still must have 5 asterisks in the middle.

Example 3

Input: s = "1(234)567-890"

Output: "*-*-7890"

s is a phone number. There are 10 digits, so the local number is 10 digits and the country code is 0 digits. Thus, the resulting masked number is "- -7890".

Constraints

s is either a valid email or a phone number.
If s is an email:

8 <= s.length <= 40 s consists of uppercase and lowercase English letters and exactly one '@' symbol and '.' symbol.

8 <= s.length <= 40
s consists of uppercase and lowercase English letters and exactly one '@' symbol and '.' symbol.
If s is a phone number:

10 <= s.length <= 20 s consists of digits, spaces, and the symbols '(', ')', '-', and '+'.

10 <= s.length <= 20
s consists of digits, spaces, and the symbols '(', ')', '-', and '+'.

Solution Approach

Detect Input Type

Check if s contains '@' to classify it as an email; otherwise, treat it as a phone number. This initial string inspection prevents misclassification and directs the correct masking logic.

Email Masking Strategy

Split the email into name and domain. Convert both to lowercase. Replace the middle characters of the name with five asterisks, keeping only the first and last character visible. Concatenate the masked name with the domain to produce the final output.

Phone Number Masking Strategy

Remove all characters except digits. Determine the country code length by subtracting 10 from the total digits. Prepend asterisks for the country code if present. Mask all local digits except the last four, maintaining the standard formatting with dashes.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

Time complexity is O(n) because each character in s is processed once for classification and masking. Space complexity is O(n) for storing intermediate results and the final masked string.

What Interviewers Usually Probe

Look for immediate input classification to avoid processing errors.
Check string lowercasing and proper insertion of asterisks for emails.
Verify correct digit masking and country code handling for phone numbers.

Common Pitfalls or Variants

Common pitfalls

Incorrectly counting characters in short email names and skipping the required five asterisks.
Failing to remove non-digit characters before phone number masking.
Mixing up local digits and country code leading to an incorrect masked output.

Follow-up variants

Masking emails with multiple subdomains and ensuring the domain remains intact.
Handling international phone numbers with varying country code lengths.
Masking hybrid strings that mix email and phone formatting and require conditional logic.

FAQ

What is the main pattern used in Masking Personal Information?

The primary pattern is string-driven manipulation: detect type, transform characters, and insert asterisks according to email or phone rules.

How many characters are replaced in email names?

Always replace the middle section of the email name with exactly five asterisks, regardless of the name length.

Do I need to preserve the original case of letters?

No, all email characters should be converted to lowercase to standardize the masked output.

How are phone numbers with country codes masked?

Mask all digits except the last four of the local number, prepend asterisks for any country code, and maintain formatting with dashes.

Can this approach handle both emails and phone numbers in a single function?

Yes, by first classifying the input using the presence of '@', then applying the respective masking strategy for each type.

terminal

Solution

Solution 1: Simulation

According to the problem description, we can first determine whether the string $s$ is an email or a phone number, and then handle it accordingly.

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class Solution:
    def maskPII(self, s: str) -> str:
        if s[0].isalpha():
            s = s.lower()
            return s[0] + '*****' + s[s.find('@') - 1 :]
        s = ''.join(c for c in s if c.isdigit())
        cnt = len(s) - 10
        suf = '***-***-' + s[-4:]
        return suf if cnt == 0 else f'+{"*" * cnt}-{suf}'

Continue Practicing

#830 positions of large groups #833 find and replace in string #828 count unique characters of all substrings of a given string