1 class Solution {
 2     public int numUniqueEmails(String[] emails) {
 3         Set<String> set = new HashSet<>();
 4         for (String email : emails) {
 5             String localNamesWithoutPoint = email.split("@")[0].replaceAll("[.]", "");
 6             String result = localNamesWithoutPoint.split("\\+")[0] + "@" + email.split("@")[1];
 7             set.add(result);
 8         }
 9         return set.size();
10     }
11 }

 1 class Solution {
 2     public int numUniqueEmails(String[] emails) {
 3         Set<String> emails_set = new HashSet<>();
 4         for(String email : emails) {
 5             int start = email.indexOf('+');
 6             int end = email.indexOf('@');
 7             String localName = email.substring(0, start);
 8             localName = localName.replace(".", "");
 9             String domainName = email.substring(end, email.length());
10             emails_set.add(localName + domainName);
11         }
12         return emails_set.size();
13     }
14 }

 1 class Solution {
 2     public int numUniqueEmails(String[] emails) {
 3         if (emails == null) return 0;
 4         HashSet<String> unique = new HashSet<String>();
 5         for (String email : emails) {
 6             unique.add(realEmail(email));
 7         }
 8         return unique.size();
 9     }
10
11     public String realEmail(String email) {
12         char[] impl = email.toCharArray();
13         boolean metAt = false;
14         boolean metPlus = false;
15         int cur = 0, dst = 0;
16         while (cur < impl.length) {
17             if (metAt) {
18                 impl[dst++] = impl[cur++];
19             } else {
20                 switch (impl[cur]) {
21                     case '.':
22                         cur++;
23                         break;
24                     case '+':
25                         metPlus = true;
26                         cur++;
27                         break;
28                     case '@':
29                         metAt = true;
30                         impl[dst++] = impl[cur++];
31                         break;
32                     default:
33                         if (metPlus) {
34                             cur++;
35                         } else {
36                             impl[dst++] = impl[cur++];
37                         }
38                 }
39             }
40         }
41         return new String(impl, 0, dst);
42     }
43 }