Question

I have a program which simply removes duplicate elements of a character array using HashSet.

Here is my program:

import java.util.Arrays;
import java.util.HashSet;

import java.util.Set;

public class MainClass {
    public static void main(String[] arg) {
        double sT = System.nanoTime();
        Character[] data = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
                'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
                'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f',
                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
                's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd',
                'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
                'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b',
                'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
                'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
                'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
                'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
                'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
                'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                'u', 'v', 'w', 'x', 'y', 'z' };

        Set<Character > uniqueSet = new HashSet<Character>(Arrays.asList(data));

         Character[] strArr = new Character[uniqueSet.size()];
         uniqueSet.toArray(strArr);

            for(Character str:strArr){
                System.out.println(str);
            }


        System.out.println(System.nanoTime() - sT);

    }

}

It gives the desired output. But problem is execution time. Is there any ways that I can implement in my program to reduce its execution time?

Answer 1

As the different types of elements that you can have is really small, you can easily use a simple array instead of a hashset(an approach similar to set or counting sort). If you only care for the non-capital English letters declare an array boolean met[26];, if you need to be able to support all characters use an boolean met[256];.

Than iterate over the array and only add a character to the result if its met value is false. When adding the character to the result don’t forget to mark it as used.

No hashing involved and thus – better performance.

EDIT: as it seems there is some confusion with what I mean I will try to add a code sample

boolean met[] = new boolean[256]; // Replace 256 with the size of alphabet you are using
List<Character> res = new ArrayList<Character>();
for(Character c:data){
  int int_val = (int)c.charValue();
  if (!met[int_val]) {
     met[int_val] = true;
     res.add(c);
  }
}

// res holds the answer.