Masking Personal Information - Practice Coding Problems

Masking Personal Information - Problem

String Medium

You are given a personal information string s, representing either an email address or a phone number. Return the masked personal information using the below rules.

Email address:
An email address is:
• A name consisting of uppercase and lowercase English letters, followed by
• The '@' symbol, followed by
• The domain consisting of uppercase and lowercase English letters with a dot '.' somewhere in the middle (not the first or last character).

To mask an email:
• The uppercase letters in the name and domain must be converted to lowercase letters.
• The middle letters of the name (i.e., all but the first and last letters) must be replaced by 5 asterisks "*****".

Phone number:
A phone number is formatted as follows:
• The phone number contains 10-13 digits.
• The last 10 digits make up the local number.
• The remaining 0-3 digits, in the beginning, make up the country code.
• Separation characters from the set {'+', '-', '(', ')', ' '} separate the above digits in some way.

To mask a phone number:
• Remove all separation characters.
• The masked phone number should have the form:
"***-***-XXXX" if the country code has 0 digits.
"+*-***-***-XXXX" if the country code has 1 digit.
"+**-***-***-XXXX" if the country code has 2 digits.
"+***-***-***-XXXX" if the country code has 3 digits.
"XXXX" is the last 4 digits of the local number.

Input & Output

Example 1 — Email Masking

$ Input: s = "[email protected]"

› Output: "l*****[email protected]"

💡 Note: Email detected by '@' symbol. Convert to lowercase, mask middle of name 'LeetCode' → 'l*****e', keep domain 'leetcode.com'

Example 2 — Phone with Country Code

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

› Output: "+*-***-***-7890"

💡 Note: Phone number with 11 digits total. Country code = 1 digit, local number last 10 digits. Format: +*-***-***-XXXX where XXXX = 7890

Example 3 — Simple Phone

$ Input: s = "123-45-6789"

› Output: "***-***-6789"

💡 Note: Phone number with exactly 10 digits. No country code (0 digits). Format: ***-***-XXXX where XXXX = 6789

Constraints

s is either a valid email or a valid phone number
If s is an email: 3 ≤ s.length ≤ 40
If s is a phone number: 10 ≤ s.length ≤ 20

Visualization

Tap to expand

Understanding the Visualization

Input

Email or phone number string

Type Detection

Check for '@' symbol to determine type

Apply Masking

Email: mask name middle, Phone: format with asterisks

Key Takeaway

🎯 Key Insight: Use '@' symbol for instant type detection, then apply appropriate masking rules

Asked in

G Google 15 a Amazon 12 f Facebook 8

The key insight is to use the '@' symbol to distinguish between email and phone number, then apply type-specific masking rules. For emails, convert to lowercase and mask the middle characters of the name with 5 asterisks. For phone numbers, extract digits and format based on country code length. Best approach uses string operations for O(n) time and O(n) space.

Common Approaches

Approach	Time	Space	Notes
✓ Character-by-Character Processing	O(n)	O(n)	Manually check each character to identify type and build masked result
String Operations Approach	O(n)	O(n)	Use built-in string methods for efficient type detection and masking

Character-by-Character Processing — Algorithm Steps

Scan each character to find '@' symbol
If email: manually extract name, domain and mask middle characters
If phone: manually extract digits and format based on country code length

Visualization

Tap to expand

Step-by-Step Walkthrough

Scan Characters

Check each character for '@' to identify type

Extract Parts

Split email at '@' or extract digits from phone

Apply Masking

Replace middle characters with asterisks

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

char* solution(char* s) {
    char* result = malloc(50 * sizeof(char));
    
    if (strchr(s, '@') != NULL) {
        // Email masking
        char* email = malloc(strlen(s) + 1);
        strcpy(email, s);
        
        // Convert to lowercase
        for (int i = 0; email[i]; i++) {
            email[i] = tolower(email[i]);
        }
        
        char* atPos = strchr(email, '@');
        int nameLen = atPos - email;
        
        if (nameLen <= 2) {
            strcpy(result, email);
        } else {
            result[0] = email[0];
            strcpy(result + 1, "*****");
            result[6] = email[nameLen - 1];
            strcpy(result + 7, atPos);
        }
        
        free(email);
    } else {
        // Phone masking
        char digits[20];
        int digitCount = 0;
        
        for (int i = 0; s[i]; i++) {
            if (isdigit(s[i])) {
                digits[digitCount++] = s[i];
            }
        }
        digits[digitCount] = '\0';
        
        int countryCodeLen = digitCount - 10;
        char lastFour[5];
        strncpy(lastFour, digits + digitCount - 4, 4);
        lastFour[4] = '\0';
        
        if (countryCodeLen == 0) {
            sprintf(result, "***-***-%s", lastFour);
        } else if (countryCodeLen == 1) {
            sprintf(result, "+*-***-***-%s", lastFour);
        } else if (countryCodeLen == 2) {
            sprintf(result, "+**-***-***-%s", lastFour);
        } else {
            sprintf(result, "+***-***-***-%s", lastFour);
        }
    }
    
    return result;
}

int main() {
    char s[100];
    fgets(s, sizeof(s), stdin);
    s[strcspn(s, "\n")] = 0;
    
    char* result = solution(s);
    printf("%s\n", result);
    free(result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through the input string of length n

✓ Linear Growth

Space Complexity

O(n)

Store the result string and intermediate character arrays

⚡ Linearithmic Space

35.4K Views

Medium Frequency

~15 min Avg. Time

892 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Character-by-Character Processing — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler