929. Unique Email Addresses

Every email consists of a local name and a domain name, separated by the @ sign.

For example, in alice@leetcode.com, alice is the local name, and leetcode.com is the domain name.

Besides lowercase letters, these emails may contain '.'s or '+'s.

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. For example, "alice.z@leetcode.com" and "alicez@leetcode.com" forward to the same email address. (Note that this rule does not apply for 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, for example m.y+name@email.com will be forwarded to my@email.com. (Again, this rule does not apply for domain names.)

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

Given a list of emails, we send one email to each address in the list. How many different addresses actually receive mails?

Example 1:

Input: ["test.email+alex@leetcode.com","test.e.mail+bob.cathy@leetcode.com","testemail+david@lee.tcode.com"]
Output: 2
Explanation: "testemail@leetcode.com" and "testemail@lee.tcode.com" actually receive mails

分析：

1. 每一个字符串，去掉“.”, 去掉“+”后面，“@”前面的字符
2. 使用一个set来去重

class Solution {
    public int numUniqueEmails(String[] emails) {
        Set<String> emailSet = new HashSet<>();// 创建一个set
        for(String email: emails){
            String temp = standardEmail(email);// 对于每一个email
            emailSet.add(temp);// 加到set里面去重
        }
        return emailSet.size();
        
    }
    
    public String standardEmail(String email){
        String userName1 = email.substring(0, email.indexOf("@"));
        String userName2 = userName1.replace(".", "");
        if(userName2.contains("+"))// 如果有“+”，那么就去掉后面的字符
            userName2 = userName2.substring(0, userName2.indexOf("+"));
        String finalEmail = userName2 + email.substring(email.indexOf("@"));//连接为标准email
        return finalEmail;
    }
}