LeetCode From Easy To Hard No10[Easy]: Unique Email Addresses 邮件地址的唯一性

very 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

 

Note:

• 1 <= emails[i].length <= 100
• 1 <= emails.length <= 100
• Each emails[i] contains exactly one '@' character.
• All local and domain names are non-empty.
• Local names do not start with a '+' character.

题目分析：给定一个email address数组, 输出有多少个不同的email adress，Email Adress 以“@”为分割点

①在"@"左边，假如出现"."，则默认忽略，比如c.o.d.e@qq.com.cn其实等价于code@qq.com.cn；假如出现"+"， 则"+"到"@"之间的内容则全部忽略，比如c.o.d.e+love@qq.com.c+n其实等价于code@qq.com.c+n; 

②在"@"右边，假如出现"."和"+"，就不会有什么变化。

利用Set集合，里边不包含重复元素的特性进行去重：
 

import java.util.HashSet;
import java.util.Set;

class Solution {
    public static int numUniqueEmails(String[] emails) {
        Set<String> set = new HashSet<String>(); // 利用set元素
        for (String e : emails) {
            int atIndex = e.indexOf("@"); // 找到@所在的索引
            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < atIndex; i++) { // 只需要循环@前边的字符
                if (e.charAt(i) == '.') continue; // 遇到“.”就直接进行下一轮循环
                if (e.charAt(i) == '+') { // 遇到“+”则退出循环
                    break;
                } else {
                    sb.append(e.charAt(i));
                }
            }
            set.add(sb.append("@").append(e.substring(atIndex)).toString()); // 拼接“@”和“@”后边的字符，然后添加进Set集合中。
        }
        return set.size();
    }

    public static void main(String[] args) {
        String[] emails = {"test.email+alex@leetcode.com", "test.email@leetcode.com"};
        System.out.println(new Solution().numUniqueEmails(emails));
    }
}