leetcode讲解--929. Unique Email Addresses

929. Unique Email Addresses

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

For example, in [e-mail], 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, "[e-mail]" and "[e-mail]" 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 [e-mail] will be forwarded to [e-mail]. (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: ["[e-mail]","[e-mail]","[e-mail]"]
Output: 2
Explanation: "[e-mail]" and "[e-mail]" actually receive mails

Note:

• 1 <= emails[i].length <= 100
• 1 <= emails.length <= 100
• Each emails[i] contains exactly one '@' character.

这道题最重要的思想是对不同的字符串段采用不同的算法，这样就能简化对单个区间的处理。

Java代码

class Solution {
        public int numUniqueEmails(String[] emails) {
        Set<String> set = new HashSet<>();
        for(String s:emails){
            int indexOfAt = s.indexOf("@");
            StringBuilder stringBuilder = new StringBuilder();
            Boolean flag = false;
            for(int i=0;i<indexOfAt;i++){
                if(flag)
                    continue;
                if(s.charAt(i)=='+'){
                    flag = true;
                    continue;
                }
                if(s.charAt(i)!='.'){
                    stringBuilder.append(s.charAt(i));
                }
            }
            for(int i=indexOfAt;i<s.length();i++){
                stringBuilder.append(s.charAt(i));
            }
            set.add(stringBuilder.toString());
        }

        return set.size();
    }
}