Question

Using Java

Write a program that reads a file of numbers of type int and outputs all of those numbers to another file, but without any duplicate numbers. You should assume that the input file is sorted from smallest to largest with one number on each line. After the program is run, the output file should contain all numbers that are in the original file, but no number should appear more than once. The numbers in the output file should also be sorted from smallest to largest with one number on each line.

Your program should not assume that there is a fixed number of entries to be read, but should be able to work with any number of entries in both the input and output files.

This means that you should not use arrays, lists, arraylists,
linked lists, sets, maps, trees, or any other multi-element data structure.

Instead, your program should read in and write out numbers from the input and output files at the same time, eliminating duplicates from the output file as you go.

Your program should obtain both file names from the user. For the original (input) file, create a text file that stores one number per line with several duplicates in sorted order. The output file should be created by your program. When completed, your program should display on the console:

1. a count of numbers in the input file
2. a count of the numbers in the output file
3. and the number of duplicates found in the input file

Example:

  Input File             Output File  
  Contents               Contents
     1                      1
     3                      3
     3                      60
     3                      75
     60                     80
     60                     100
     75                     130
     75                     140
     75                     985
     80                     1000
     80
     100
     130
     140
     985
     985
     985
     1000

Sample console dialog, where input from the user is underlined in italics

  Enter input file name or full path: numbers.txt
  Enter output file name or full path: output.txt
  There were 18 numbers input, 10 output, and 8 duplicates. 

Answer 1

import java.io.File;
import java.io.PrintWriter;
import java.util.Scanner;

public class RemoveDupInFile {
   public static void main(String[] args) throws Exception {
       //opening file to read
       Scanner sc = new Scanner(new File("input.txt"));
       PrintWriter pw = new PrintWriter(new File("output.txt"));
       int prev = -1, num;
       num = sc.nextInt();
       while (sc.hasNext()) {
           //checking if it is not previous number
           if (num != prev) {
               pw.println(num);
           }
           //making current num as prev
           prev = num;
           //reading next num
           num = sc.nextInt();
       }
       pw.println(num);
       pw.close();
   }
}

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