问题：
英文：
Every email consists of a local name and a domain name, separated by the @ sign.
For example, in [email protected], 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, "[email protected]" and "[email protected]" 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 [email protected] will be forwarded to [email protected]. (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?
中文：
每封电子邮件都包含本地名称和域名，以@符号分隔。
例如，在[email protected]中，alice是本地名称，leetcode.com是域名。
除了小写字母，这些电子邮件可能包含'.'或'+'。
如果在电子邮件地址的本地名称部分中的某些字符之间添加句点（'.'），则将发送的邮件将转发到本地名称中没有（'.'）的同一地址。例如，“[email protected]”和“[email protected]”转发到同一电子邮件地址。 （请注意，此规则不适用于域名。）
如果在本地名称中添加加号（'+'），则会忽略第一个加号后面的所有内容。这允许过滤某些电子邮件，例如[email protected]将转发到[email protected]。 （同样，此规则不适用于域名。）
可以同时使用这两个规则。
给定电子邮件列表，我们会向列表中的每个地址发送一封电子邮件。有多少不同的地址实际接收邮件？
Example 1:
Input: ["[email protected]","[email protected]","[email protected]"] Output: 2 Explanation: "[email protected]" and "[email protected]" actually receive mails
Note:
1 <= emails[i].length <= 1001 <= emails.length <= 100- Each
emails[i]contains exactly one'@'character.
解决方法：
创建一个Set，因为Set中的元素不重复。
分别按规则处理本地名称和域名，再拼接，并放入Set中。
最后Set中元素的个数就为可能发送的地址个数。
package cn.leetcode.easy;
import java.util.HashSet;
import java.util.Set;
/**
* Every email consists of a local name and a domain name, separated by the @ sign.
*
* For example, in [email protected], 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, "[email protected]" and "[email protected]" 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 [email protected] will be forwarded to [email protected].
* (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?
*
* @author kimtian
*/
public class UniqueEmailAddresses {
/**
* 邮件地址个数计算
*
* @param emails 输入的邮件地址
* @return 可能发送到的邮件地址个数
*/
public static int numUniqueEmails(String[] emails) {
//创建一个set存放处理后的邮件地址，因为set中不会有重复的元素
Set<String> emailSet = new HashSet<>();
// 题干备注emails数组的长度为>=100且<=1
if (emails.length >= 1 && emails.length <= 100) {
//循环emails数组，拿到每一个email地址
for (String string : emails) {
//本地名称为邮件地址@前的部分
String localName = string.substring(0, string.indexOf("@"));
//如果有(+)则只取(+)前的邮箱地址
if (localName.contains("+")) {
localName = localName.substring(0, localName.indexOf("+"));
}
//如果有(.)则将其去除
localName = localName.replace(".", "");
//域名
String domainName = string.substring(string.indexOf("@"));
//将本地名称和域名再次拼接
string = localName + domainName;
//存放在set中，set会帮忙直接过滤掉重复地址
emailSet.add(string);
}
}
return emailSet.size();
}
/**
* 测试
*
* @param args
*/
public static void main(String[] args) {
String[] aa = {"[email protected]", "[email protected]", "[email protected]"};
System.out.println(numUniqueEmails(aa));
}
}