Print Duplicate element from an array

1.By using HashMap<key,value> under collection framework concept we can find the duplicate ones

Example

import java.util.HashMap;
import java.util.Map;

class Employee
{
    public static void main(String args[])
    {
        int arr[] = {1,2,2,2,3,4,4 };
        int size =arr.length;
        HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();
        for(int i=0;i<size;i++)
        {
            if(map.containsKey(arr[i]))
                map.put(arr[i],0);
            else
                map.put(arr[i],1);
        }
        for(Map.Entry<Integer,Integer> entry : map.entrySet())
        {
            if(entry.getValue() == 0)
                System.out.print(entry.getKey()+ " ");
        }
    }
}

Time Complexity: O(N)
Auxiliary Space: O(N)

2.If you dont need you use collection mean then we can achieve the result by using merge sort and bubble sort algorthim

merge sort — → for sorting the unsorted array

Bubble sort — — -> for Printing duplicate element from the sorted array

import java.util.Arrays;

class Employee
{
    public static  void main(String args[])
    {
        int[] values = {4,3,3,2,2,1,4};
        int size = values.length;
        sort(values,0,size-1);

        System.out.println("Array is sorted"+Arrays.toString(values));

        int[]  temp = new int[size];
        int j = 0;
        for(int i=0;i<size-1;i++)
        {
            if(values[i] == values[i+1])
            {
                temp[j] = values[i];
                j++;
            }
        }


        for(int i=0;i<j;i++)
        {
            System.out.println("Sorted Result--"+temp[i]);
        }


    }
    public static void sort(int values[],int low,int high)
    {
        if(low < high)
        {
            int middlelement = low + (high-low)/2;
            sort(values,low,middlelement);
            sort(values,middlelement+1,high);
            merge(values,low,middlelement,high);
        }
    }
    public static void merge(int[] values,int low,int middle,int high)
    {
        int n1 = middle - low +1;
        int n2 = high - middle;

        int[] L1 = new int[n1];
        int[] L2 = new int[n2];

        for(int i=0;i<n1;i++)
            L1[i] = values[low+i];
        for(int i=0;i<n2;i++)
            L2[i] = values[middle+1+i];

        int i=0,j=0,k=low;
        while (i<n1 && j<n2)
        {
            if(L1[i] <= L2[j])
            {
                values[k] = L1[i];
                i++;
                k++;
            }
            else
            {
                values[k] = L2[j];
                j++;
                k++;
            }
        }
        while (i<n1)
        {
            values[k] = L1[i];
            i++;
            k++;
        }
        while (j<n2)
        {
            values[k] = L2[j];
            j++;
            k++;
        }
    }
}