Unique Email Addresses LeetCode Solution

Problem – Unique Email Addresses

Every valid email consists of a local name and a domain name, separated by the '@' sign. Besides lowercase letters, the email may contain one or more '.' or '+'.

  • For example, in "[email protected]""alice" is the local name, and "leetcode.com" is the domain name.

If you add periods '.' between some characters in the local name part of an email address, mail sent there will be forwarded to the same address without dots in the local name. Note that this rule does not apply to domain names.

If you add a plus '+' in the local name, everything after the first plus sign will be ignored. This allows certain emails to be filtered. Note that this rule does not apply to domain names.

It is possible to use both of these rules at the same time.

Given an array of strings emails where we send one email to each emails[i], return the number of different addresses that actually receive mails.

Example 1:

Input: emails = ["[email protected]","[email protected]","[email protected]"]
Output: 2
Explanation: "[email protected]" and "[email protected]" actually receive mails.

Example 2:

Input: emails = ["[email protected]","[email protected]","[email protected]"]
Output: 3


  • 1 <= emails.length <= 100
  • 1 <= emails[i].length <= 100
  • emails[i] consist of lowercase English letters, '+''.' and '@'.
  • Each emails[i] contains exactly one '@' character.
  • All local and domain names are non-empty.
  • Local names do not start with a '+' character.
  • Domain names end with the ".com" suffix.

Unique Email Addresses LeetCode Solution in Java

    public int numUniqueEmails(String[] emails) {
        Set<String> normalized = new HashSet<>(); // used to save simplified email address, cost O(n) sapce.
        for (String email : emails) {
            String[] parts = email.split("@"); // split into local and domain parts.
            String[] local = parts[0].split("\\+"); // split local by '+'.
            normalized.add(local[0].replace(".", "") + "@" + parts[1]); // remove all '.', and concatenate '@' and domain.        
        return normalized.size();

Unique Email Addresses LeetCode Solution in C++

int numUniqueEmails(vector<string>& emails) {
    unordered_set<string> st;
    for(string &email : emails) {
        string cleanEmail;
        for(char c : email) {
            if(c == '+' || c == '@') break;
            if(c == '.') continue;
            cleanEmail += c;
        cleanEmail += email.substr(email.find('@'));
    return st.size();

Unique Email Addresses LeetCode Solution in Python

class Solution:
    def numUniqueEmails(self, emails):
        :type emails: List[str]
        :rtype: int
        email_set = set()
        for email in emails:
            local_name,domain_name = email.split("@")
            local_name ="".join(local_name.split('+')[0].split('.'))
            email = local_name +'@' + domain_name
        return len(email_set)
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