Find Duplicate Element in Array, Find count of duplicate element in array, remove duplicate element from array

Hello Friends,

In this article , we will learn , Three below things :-
1). How to Find Duplicate Element in array
2). How to find count of duplicate element in array.
3). How to remove duplicate element from array.
Note : It is very important tutorial for interview purpose.

Video :

It can be achieved by simple below algorithm :-
First create a collection.
now compare each element, within this collection
If collection have that element, than ignore else add this element to collection.

Below is Sample code :-

package Chandan_Java.Chandan_Java;
import java.util.*;
import org.testng.Assert;
import org.testng.annotations.Test;
import org.testng.asserts.SoftAssert;
public class PojorunExample
{
@Test
public void g()
{
int x[] = {2, 9 , 5, 2, 3, 5, 7, 9, 3, 2};
List<Integer> list = new ArrayList<Integer>();
list.add(x[0]);
for(int i =0; i<x.length; i++)
{
if(list.contains(x[i]))
{
}
else
{
list.add(x[i]);
}
}
for(int j = 0; j<list.size(); j++)
{
System.out.println(list.get(j));
}
}
}

OUTPUT :-

2
9
5
3
7

Another Way to Remove Duplicate Elements from an Array Using HashSet Class of Set Interface

public class PojorunExample
{
@Test
public void g()
{
int x[] = {2, 9 , 5, 2, 3, 5, 7, 9, 3, 2};
Set<Integer> hs = new HashSet<Integer>();
for(int i =0; i<x.length; i++)
{
hs.add(x[i]);
}
for(int z : hs)
{
System.out.println(z);
}
}
}
OUTPUT :-
2
9
5
3
7

Example to get Duplicate Emailement from an Array & Occurance of duplicate element using HashMap class of Map Interface

package Chandan_Java.Chandan_Java;

import java.util.*;
import org.testng.Assert;
import org.testng.annotations.Test;
import org.testng.asserts.SoftAssert;
public class JavaInterview
{
@Test
public void g()
{
int x[] = {2, 2, 9 , 5, 2, 3, 5, 7, 9, 3, 2};
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for(int i =0; i<x.length; i++)
{
if(map.containsKey(x[i]))
{
int t = map.get(x[i]) + 1;
map.put(x[i], t);
}
else
{
map.put(x[i], 1);
}
}
System.out.println(map);
}
}

OUTPUT :-
{2=4, 3=2, 5=2, 7=1, 9=2}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.atomic.AtomicInteger;

public class Interviewtest
{
//find the duplicate elements in the array
int count;
public static void main(String args[])
{
int arr[] = {4, 2, 2, 4, 55, 6, 99, 55};
AtomicInteger count = new AtomicInteger(1);
Set newarray = new HashSet();
for(int i =0; i<arr.length; i++)
{
if(newarray.contains(arr[i]))
{
int x = count.getAndIncrement();
//System.out.println("Element"+ " " + arr[i] + " " + x);
}
else
{
newarray.add(arr[i]);
}
for(int j =i+1; j<arr.length; j++)
{
if(arr[i]==arr[j])
{
System.out.println("Duplicate element is:->" +" "+arr[i]);
}
}
}
System.out.println(newarray);
g();
h();
}
public static void g()
{
String arr[] = new String[]{"chandan", "adhiraj", "Tina", "Cathy", "chandan", "adhiraj"};
Set duplicate = new HashSet<>();
Set nonduplicate = new HashSet<>();
for(String srting : arr)
{
/*if(!nonduplicate.contains(srting))
{
nonduplicate.add(srting);
}
else
{
duplicate.add(srting);
}*/
if(nonduplicate.contains(srting))
{
duplicate.add(srting);
}
else
{
nonduplicate.add(srting);
}
}
System.out.println(duplicate);
System.out.println(nonduplicate);
}
public static void h()
{
int arr[] = {4, 2, 2, 4, 55, 6, 99, 55};
for(int i =0; i<arr.length; i++)
{
int t = 1;
for(int j =i+1; j<arr.length; j++)
{
if(arr[i]==arr[j])
{
t = t+1;
}
}
System.out.println("Element" + " " + arr[i] + " " + "occurs" + " " + t);
}
}
}