How can I remove duplicate elements from a given array in java without using collections

Question

I have an array elements like this:

int arr[] = {1,1,2,2,3,3,4,4};

I want to remove the duplicate elements from. Searched on the internet

Answer 1

public int[] removeDuplicates(int[] arr) {
    int[] res = new int[arr.length];
    int index = 0;
    for (int num : arr) {
        if (res.indexOf(num) == -1)
            res[index++] = num;
    }
    return res;
}

This is a suboptimal solution, however it does not require any sorting of the array. I create a new array, iterate through the items in the original one and add the items to the new array if they aren't already there.

Answer 2

Use below method:

/*
 * Method to remove duplicates from array in Java, without using
 * Collection classes e.g. Set or ArrayList. Algorithm for this
 * method is simple, it first sort the array and then compare adjacent
 * objects, leaving out duplicates, which is already in the result.
 */
public static int[] removeDuplicates(int[] numbersWithDuplicates) {

    // Sorting array to bring duplicates together      
    Arrays.sort(numbersWithDuplicates);     

    int[] result = new int[numbersWithDuplicates.length];
    int previous = numbersWithDuplicates[0];
    result[0] = previous;

    for (int i = 1; i < numbersWithDuplicates.length; i++) {
        int ch = numbersWithDuplicates[i];

        if (previous != ch) {
            result[i] = ch;
        }
        previous = ch;
    }
    return result;

}

Answer 3

public class UniqueElementinAnArray 
{

public static void main(String[] args) 
{
    int[] a = {10,10,10,10,10,100};
    int[] output = new int[a.length];
    int count = 0;
    int num = 0;

    //Iterate over an array
    for(int i=0; i<a.length; i++)
    {
        num=a[i];
        boolean flag = check(output,num);
        if(flag==false)
        {
            output[count]=num;
            ++count;
        }

    }

    //print the all the elements from an array except zero's (0)
    for (int i : output) 
    {
        if(i!=0 )
            System.out.print(i+"  ");
    }

}

/***
 * If a next number from an array is already exists in unique array then return true else false
 * @param arr   Unique number array. Initially this array is an empty.
 * @param num   Number to be search in unique array. Whether it is duplicate or unique.
 * @return  true: If a number is already exists in an array else false 
 */
public static boolean check(int[] arr, int num)
{
    boolean flag = false;
    for(int i=0;i<arr.length; i++)
    {
        if(arr[i]==num)
        {
            flag = true;
            break;
        }
    }
    return flag;
}

}

Answer 4

public static int[] removeDuplicates(int[] input){

    int j = 0;
    int i = 1;
    //return if the array length is less than 2
    if(input.length < 2){
        return input;
    }
    while(i < input.length){
        if(input[i] == input[j]){
            i++;
        }else{
            input[++j] = input[i++];
        }   
    }
    int[] output = new int[j+1];
    for(int k=0; k<output.length; k++){
        output[k] = input[k];
    }

    return output;
}

Source : http://java2novice.com/java-interview-programs/remove-duplicates-sorted-array/

Answer 5

    int flag = 0, k = 0;
    for (int i = 0; i < arr.length; i++) {
        for (int j = 0; j < arrAns.length; j++) {
            if (arr[i] == arrAns[j]) {
                flag = 0;
                break;
            }
            flag=1;
        }
        if (flag == 1) {
            arrAns[k] = arr[i];
            k++;
        }
        flag = 0;
    }

Answer 6

package practice1;

import java.util.Scanner;

public class RemoveArrayDuplicatesElements {


    public static void main(String[] args) {

        int i, j, k, size,same = 0;

        System.out.println("\nEnter array size : ");
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        size = sc.nextInt();
        int[] arr = new int[size+1];
        System.out.println("\nAccept Numbers : ");
        for (i = 0; i < size; i++)
            arr[i] = sc.nextInt();

        System.out.println("\nArray with Unique list  : ");

        for (i = 0; i < size; i++) {
              for (j = i + 1; j < size;) {
                 if (arr[j] == arr[i]) {
                     same++;
                    for (k = j; k < size; k++) {
                       arr[k] = arr[k + 1];
                    }
                    size--;
                 } else
                    j++;
              }
           }




        for (int g = 0; g < arr.length; g++) {
            System.out.println(arr[g]);
        }

    }

}