Question

Write a program which takes three lists of names, and print out all the names only once. The expected runtime should be O(n) where n is the total number of names in the lists. You don’t have to sort the list. Use appropriate data structure to store the names, so add all data to the collection only once efficiently. The read-in list method and list1, list2, list3 is given. You may assume that the expected runtime of searching or inserting into a hash table is O(1). Do not call the list's contains method, because it slows down the run time.

import java.io.*;
import java.util.*;
public class A4PrintName{
   public static List<String> readInFile(String filename){
      List<String> input = new ArrayList<>();
      try (Scanner sin = new Scanner(new FileReader(filename))){
         while (sin.hasNextLine()){
            input.add(sin.nextLine());
         }
      } catch (FileNotFoundException e){
         e.printStackTrace();
      }
      return input;
  }
   public static void main(String[] args){
      List<String> namelist1 = readInFile("A4input1.txt");
      List<String> namelist2 = readInFile("A4input2.txt");
      List<String> namelist3 = readInFile("A4input3.txt");
      Set<String> names;
      //your code starts here... you may write any function where you need.
   }
}

list 1:

Amy
Andy
Anna
Ben
Benjamin
Catherine
Emma
James
Jessie
Jennifer
John
Karen
Kelly
Kyle
Lena
Liam
Mary
Mia
Steve
William

list 2:

Amy
Andy
Anne
Ben
Benjamin
Catherine
David
Emma
James
Jessie
Jennifer
Jenny
John
Karen
Kelly
Kyle
Mary
Mia
Selina
Tina
William

list 3:

Amy
Ana
Anne
Dave
George
Selina
Shawn
William

Answer 1

import java.io.*;
import java.util.*;
public class Main{
public static List<String> readInFile(String filename){
List<String> input = new ArrayList<>();
try (Scanner sin = new Scanner(new FileReader(filename))){
while (sin.hasNextLine()){
input.add(sin.nextLine());
}
} catch (FileNotFoundException e){
e.printStackTrace();
}
return input;
}
public static void main(String[] args){
List<String> namelist1 = readInFile("A4input1.txt");
List<String> namelist2 = readInFile("A4input2.txt");
List<String> namelist3 = readInFile("A4input3.txt");
Set<String> names=new HashSet<String>();//create hashset
names.addAll(namelist1);//add all values using addAll method in namelist1
names.addAll(namelist2);//in the same manner add for namelist2,namelist3
names.addAll(namelist3);
System.out.println(names);//print the names
/*You can also use loop upto how many values are there and add each element separately*/
  
}
}

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