Rust LeetCode 练习：929 Unique Email Addresses

LeetCode 929 Unique Email Addresses

题目大意：邮箱地址格式为[本地名]@[域名]，其中[本地名]存在+和.两种特殊状况。如今输入一组邮箱地址，要求进行以下处理，而后输出非重复的地址数量。

• 对+，忽略其后至@前的全部字符。
• 对.，忽略之。

1. 朴素实现：（1）过滤本地名中+至@以前全部字符。（2）过滤本地名中.字符。（3）将处理好的地址列表进行去重操做。（4）返回最终数量。 Runtime: 4 ms Memory Usage: 892.9 KB。

   pub fn num_unique_emails(emails: Vec<String>) -> i32 {
       let mut num = 0;
       let mut process_emails = vec![];
       process_emails.clone_from(&emails);
       let mut process_emails = process_emails
           .iter_mut()
           .map(|s| {
               if let Some(plus) = s.find('+') {
                   if let Some(at) = s.find('@') {
                       if at > plus {
                           s.replace_range(plus..at, "");
                       }
                   }
               }
               s
           })
           .map(|s| {
               while let Some(dot) = s.find('.') {
                   if let Some(at) = s.find('@') {
                       if dot < at {
                           s.replace_range(dot..(dot + 1), "");
                       } else {
                           break;
                       }
                   }
               }
               s
           })
           .collect::<Vec<_>>();
       process_emails.sort();
       process_emails.dedup_by(|a, b| a.eq(&b));
       process_emails.len() as i32
   }
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2. 优化：利用HashSet去重。 Runtime: 4 ms Memory Usage: 921.6 KB

   pub fn num_unique_emails(emails: Vec<String>) -> i32 {
       use std::collections::HashSet;
       let mut unique_emails = HashSet::<String>::new();
       for email in &emails {
           let email: Vec<&str> = email.split('@').collect::<Vec<_>>();
           let mut local_name = email[0].to_owned();
           if let Some(plus) = local_name.find('+') {
               local_name.replace_range(plus..local_name.len(), "");
           };
           local_name = local_name.replace('.', "");
           unique_emails.insert(local_name + email[1]);
       }
       unique_emails.len() as i32
   }
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3. 代码简化：利用for_each迭代器。使人困惑的是，内存暴涨到2.6 MB。 Runtime: 4 ms Memory Usage: 2.6 MB

   pub fn num_unique_emails(emails: Vec<String>) -> i32 {
       use std::collections::HashSet;
       let mut unique_emails = HashSet::<String>::new();
       emails.into_iter().for_each(|s| {
           let email = s.split("@").collect::<Vec<&str>>();
           let mut local_name = email[0].to_owned();
           if let Some(plus) = local_name.find('+') {
               local_name.replace_range(plus.., "");
           }
           local_name = local_name.replace('.', "");
           unique_emails.insert(local_name + email[1]);
       });
       unique_emails.len() as i32
   }
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