uniqueEmails.js

// https://leetcode.com/problems/unique-email-addresses/solution/

let numUniqueEmails = function (emails) {
  // hash set to store all the unique emails
  let uniqueEmails = new Set();

  emails.forEach((email) => {
    let cleanMail = [];

    // iterate over each character in email
    for (let i = 0; i < email.length; ++i) {
      let currChar = email.charAt(i);

      // stop adding characters to localName
      if (currChar === '+' || currChar === '@') break;

      // add this character if not '.'
      if (currChar !== '.') cleanMail.push(currChar);
    }

    // compute domain name (substring from end to '@')
    let domainName = [];

    for (i = email.length - 1; i >= 0; --i) {
      let currChar = email.charAt(i);
      domainName.push(currChar);
      if (currChar == '@') break;
    }

    domainName = domainName.reverse().join('');
    cleanMail = cleanMail.join('');

    uniqueEmails.add(cleanMail + domainName);
  });

  return uniqueEmails.size;
};