Removing left sided duplicates from array

Question

I'm trying to find mistakes in my code and i wonder if you could help me. My task is to write a method that would take an array as an input and return this array without left duplicates(last numbers stay). My code doesn't work in case when input is( 1,2,1,2,1,2,3 ) It returns (1, 1, 2, 3) instead of 1,2,3. Here is the code

     public static int [] solve(int [] arr){
          boolean check=false;
        ArrayList<Integer> test = new ArrayList<>(); // idk how to compete this task without ArrayList
          for (int i = 0; i < arr.length; i++) { // Here i pass my array to ArrayList
             test.add(arr[i]);
             }
             
            while(check==false) {
                for (int i = 0; i < test.size(); i++) {
                   for (int j = i + 1; j < test.size(); j++) { // Somewhere here must be my mistake that i can't find 
                       check=true;
                       if (test.get(i) == test.get(j)) {
                           test.remove(i);
                          check=false;
                       }
                   }
               }
           }
      // i created second array to return array without duplcates. 
           int arr2[];
             arr2=new int[test.size()];
             for(int i=0;i<arr2.length;i++){
                 arr2[i]=test.get(i);
             }
        
        return arr2;
    
       }
     }

I tried to complete this task on my own, so i didnt use Google to get help until now. If you know how to improve my code feel free to change everything you want to. Thank you in advance!

Answer 1

A simple way will be to

1. Add the numbers of the array in reverse order to a LinkedHashSet in order to keep only unique numbers as well as to preserve the last entry of each unique number.

2. Create a List out of the LinkedHashSet.

3. Reverse the List using Collections#reverse.

   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.LinkedHashSet;
   import java.util.List;
   import java.util.Set;
   
   public class Main {
       public static void main(String[] args) {
           Set<Integer> set = new LinkedHashSet<>();
           int[] arr = { 7, 7, 4, 5, 7, 2, 7 };
   
           // Add the numbers of the array in reverse order to a LinkedHashSet in order to remove
           // duplicates as well as to preserve the last entry of each unique number.
           for (int i = arr.length - 1; i >= 0; i--) {
               set.add(arr[i]);
           }
   
           // Create a List out of the LinkedHashSet
           List<Integer> list = new ArrayList<>(set);
   
           // Reverse the List
           Collections.reverse(list);
   
           // Display the result
           System.out.println(list);
       }
   }
   

Output:

[4, 5, 2, 7]