929. Unique Email Addresses(python+cpp)

题目:

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

解释:
很简单的字符串解析的题目,善于使用split(),即可,c++没有split(),可以使用istringstream实现类似的效果。
python代码:

class Solution:
    def numUniqueEmails(self, emails):
        """
        :type emails: List[str]
        :rtype: int
        """
        _set=set()
        for email in emails:
            localName,domainName=email.split('@')
            localName=localName.split('+')[0].replace('.','')
            _set.add(localName+'@'+domainName)
        return len(_set)

c++代码:

#include 
#include
#include
using namespace std;
class Solution {
public:
    int numUniqueEmails(vector<string>& emails) {
        set<string> _set;
        for(auto email:emails)
        {
            string new_email="";
            string word="";
            istringstream emailstream(email);
            int count=0;
            while(getline(emailstream,word,'@'))
            {
                if (count==0)
                {
                    int cnt=0;
                    istringstream localName(word);
                    string local="";
                    while(getline(localName,local,'+') && cnt==0)
                    {
                        cnt++;
                        //C++中要从string中删除所有某个特定字符, 可用如下代码
                        //str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());
                        //python直接替换成空字符就行,c++不能替换为空字符...
                        local.erase(remove(local.begin(),local.end(),'.'),local.end());
                        new_email+=local;
                    }
                }
                else
                    new_email+="@"+word;
                count++;
            }
            _set.insert(new_email);
        }
        return _set.size();
    }
};

总结:
C++中要从string中删除所有某个特定字符, 可用如下代码
str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());
因为remove()函数只是把要删除的元素后面的元素往前移动,remove()之后的字符串长度是不变的,后面几个元素是重复的,所以还需要erase()掉。
使用istringstream一定要#include

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