Java Array, Finding Duplicates

Question

I have an array, and am looking for duplicates.

duplicates = false;
for(j = 0; j < zipcodeList.length; j++){
    for(k = 0; k < zipcodeList.length; k++         


        

Answer 1

Don't use == use .equals.

try this instead (IIRC, ZipCode needs to implement Comparable for this to work.

boolean unique;
Set<ZipCode> s = new TreeSet<ZipCode>();
for( ZipCode zc : zipcodelist )
    unique||=s.add(zc);
duplicates = !unique;

Answer 2

You can also work with Set, which doesn't allow duplicates in Java..

    for (String name : names)
    {         
      if (set.add(name) == false) 
         { // your duplicate element }
    }

using add() method and check return value. If add() returns false it means that element is not allowed in the Set and that is your duplicate.

Answer 3

@andersoj gave a great answer, but I also want add new simple way

    private boolean checkDuplicateBySet(Integer[] zipcodeList) {
        Set<Integer> zipcodeSet = new HashSet(Arrays.asList(zipcodeList));
        if (zipcodeSet.size() == zipcodeList.length) {
            return true;
        }
        return false;
    }

In case zipcodeList is int[], you need convert int[] to Integer[] first(It not auto-boxing), code here

Complete code will be:

    private boolean checkDuplicateBySet2(int[] zipcodeList) {
        Integer[] zipcodeIntegerArray = new Integer[zipcodeList.length];
        for (int i = 0; i < zipcodeList.length; i++) {
            zipcodeIntegerArray[i] = Integer.valueOf(zipcodeList[i]);
        }

        Set<Integer> zipcodeSet = new HashSet(Arrays.asList(zipcodeIntegerArray));
        if (zipcodeSet.size() == zipcodeList.length) {
            return true;
        }
        return false;
    }

Hope this helps!

Answer 4

Print all the duplicate elements. Output -1 when no repeating elements are found.

import java.util.*;

public class PrintDuplicate {

    public static void main(String args[]){
        HashMap<Integer,Integer> h = new HashMap<Integer,Integer>();


        Scanner s=new Scanner(System.in);
        int ii=s.nextInt();
        int k=s.nextInt();
        int[] arr=new  int[k];
        int[] arr1=new  int[k];
        int l=0;
        for(int i=0; i<arr.length; i++)
            arr[i]=s.nextInt();
        for(int i=0; i<arr.length; i++){
            if(h.containsKey(arr[i])){
                h.put(arr[i], h.get(arr[i]) + 1);
                arr1[l++]=arr[i];
            } else {
                h.put(arr[i], 1);
            }
        }
        if(l>0)
        { 
            for(int i=0;i<l;i++)
                System.out.println(arr1[i]);
        }
        else
            System.out.println(-1);
    }
}

Answer 5

public static ArrayList<Integer> duplicate(final int[] zipcodelist) {

    HashSet<Integer> hs = new HashSet<>();
    ArrayList<Integer> al = new ArrayList<>();
    for(int element: zipcodelist) {
        if(hs.add(element)==false) {
            al.add(element);
        }   
    }
    return al;
}

Answer 6

To check for duplicates you need to compare distinct pairs.