numUniqueEmails = function (emails) {
	const valid = emails.map(email => {
		const [local, domain] = email.split("@");
		return (
			local.split("+").shift().split(".").join("") + "@" + domain
		);
	});

	return new Set(valid).size;
}
Built-in Functions Solution
Hash Set - Unique Emails
Time O(N * K) | Space O(N)
https://leetcode.com/problems/unique-email-addresses
@param {string[]} emails
@return {number}