LeetCode之Unique Email Addresses（Kotlin）

問題： 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
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方法： 遇到"."跳過，遇到"+"跳過後面字元，遇到@忽略規則，用set儲存按規則過濾的字元，最後輸出set的size即為結果。

具體實現：

class UniqueEmailAddresses {
    fun numUniqueEmails(emails: Array<String>): Int {
        val set = mutableSetOf<String>()
        for (email in emails) {
            val sb = StringBuilder()
            var ignore = false
            var skip = false
            for (ch in email) {
                if (!ignore) {
                    if(ch == '@') {
                        ignore = true
                        skip = false
                    } else if(ch == '.' || skip) {
                        continue
                    } else if (ch == '+') {
                        skip = true
                    }
                }
                sb.append(ch)
            }
            set.add(sb.toString())
        }
        return set.size
    }
}

fun main(args: Array<String>) {
    val input = arrayOf("test.email+alex@leetcode.com","test.e.mail+bob.cathy@leetcode.com","testemail+david@lee.tcode.com")
    val uniqueEmailAddresses = UniqueEmailAddresses()
    println(uniqueEmailAddresses.numUniqueEmails(input))
}
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具體程式碼實現可以參考Github