删除文本文件中重复行的Java程序-yiteyi-C++库

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给定一个文件输入。txt。我们的任务是从中删除重复的行，并将输出保存在文件中，例如output。txt

朴素算法：

1. Create PrintWriter object for output.txt
2. Open BufferedReader for input.txt
3. Run a loop for each line of input.txt
   3.1 flag = false
   3.2 Open BufferedReader for output.txt
   3.3 Run a loop for each line of output.txt
      ->  If  line of output.txt is equal to current line of input.txt 
            -> flag = true
            -> break loop

4. Check flag, if false
     -> write current line of input.txt to output.txt
     -> Flush PrintWriter stream

5. Close resources.

要成功运行以下程序输入。txt必须存在于同一文件夹中，或提供其完整路径。

                     // Java program to remove                   
                     // duplicates from input.txt and                   
                     // save output to output.txt                   
                             
                     import                               java.io.*;                   
                             
                     public                               class                               FileOperation                   
                     {                   
                                         public                               static                               void                               main(String[] args)                               throws                               IOException                   
                                         {                   
                                         // PrintWriter object for output.txt                   
                                         PrintWriter pw =                               new                               PrintWriter(                               "output.txt"                               );                   
                             
                                         // BufferedReader object for input.txt                   
                                         BufferedReader br1 =                               new                               BufferedReader(                               new                               FileReader(                               "input.txt"                               ));                   
                             
                                         String line1 = br1.readLine();                   
                             
                                         // loop for each line of input.txt                   
                                         while                               (line1 !=                               null                               )                   
                                         {                   
                                         boolean                               flag =                               false                               ;                   
                             
                                         // BufferedReader object for output.txt                   
                                         BufferedReader br2 =                               new                               BufferedReader(                               new                               FileReader(                               "output.txt"                               ));                   
                             
                                         String line2 = br2.readLine();                   
                             
                                         // loop for each line of output.txt                   
                                         while                               (line2 !=                               null                               )                   
                                         {                   
                             
                                         if                               (line1.equals(line2))                   
                                         {                   
                                         flag =                               true                               ;                   
                                         break                               ;                   
                                         }                   
                             
                                         line2 = br2.readLine();                   
                             
                                         }                   
                             
                                         // if flag = false                   
                                         // write line of input.txt to output.txt                   
                                         if                               (!flag){                   
                                         pw.println(line1);                   
                             
                                         // flushing is important here                   
                                         pw.flush();                   
                                         }                   
                             
                                         line1 = br1.readLine();                   
                             
                                         }                   
                             
                                         // closing resources                   
                                         br1.close();                   
                                         pw.close();                   
                             
                                         System.out.println(                               "File operation performed successfully"                               );                   
                                         }                   
                     }                   

输出：

File operation performed successfully

注：如果输出。txt存在于cwd（当前工作目录）中，然后它将被上述程序覆盖，否则将创建新文件。

A. 更好的解决方案 就是使用哈希集存储每行输入。txt。As set会忽略重复的值，所以在存储行时，请检查它是否已经存在于哈希集中。将其写入输出。仅当hashset中不存在时才使用txt。

要成功运行以下程序输入。txt必须存在于同一文件夹中，或为其提供完整路径。

                     // Efficient Java program to remove                   
                     // duplicates from input.txt and                   
                     // save output to output.txt                   
                             
                     import                               java.io.*;                   
                     import                               java.util.HashSet;                   
                             
                     public                               class                               FileOperation                   
                     {                   
                                         public                               static                               void                               main(String[] args)                               throws                               IOException                   
                                         {                   
                                         // PrintWriter object for output.txt                   
                                         PrintWriter pw =                               new                               PrintWriter(                               "output.txt"                               );                   
                             
                                         // BufferedReader object for input.txt                   
                                         BufferedReader br =                               new                               BufferedReader(                               new                               FileReader(                               "input.txt"                               ));                   
                             
                                         String line = br.readLine();                   
                             
                                         // set store unique values                   
                                         HashSet<String> hs =                               new                               HashSet<String>();                   
                             
                                         // loop for each line of input.txt                   
                                         while                               (line !=                               null                               )                   
                                         {                   
                                         // write only if not                   
                                         // present in hashset                   
                                         if                               (hs.add(line))                   
                                         pw.println(line);                   
                             
                                         line = br.readLine();                   
                             
                                         }                   
                             
                                         pw.flush();                   
                             
                                         // closing resources                   
                                         br.close();                   
                                         pw.close();                   
                             
                                         System.out.println(                               "File operation performed successfully"                               );                   
                                         }                   
                     }                   