find the frequency of elements in a java array

Question

I have an int array:

{1,2,4,2,3,5,6,4,3}

How can I find frequencies of array elements like 1=1,2=2,3=2,4=4... I need a class w

Answer 1

class MapTest
{
    public static void main(String args[]){
        HashMap<Integer,Integer> h = new HashMap<Integer,Integer>();
        int arr[] = new int[]{2,2,3,3,5,6,7,9,9,0};
        for(int i=0; i<arr.length; i++){
            if(h.containsKey(arr[i])){
                h.put(arr[i], h.get(arr[i]) + 1);
            } else {
                h.put(arr[i], 1);
            }
        }
        System.out.println(h);
    }
}

Answer 2

If range of the elements of the array is specified and limited to array size, the best solution is using hash map. T(n) = O(n), auxiliary space = O(n).

public static void findCount3(int[] a){
    Map<Integer, Integer> hm = new HashMap<Integer, Integer>();     
    for(int i = 0; i < a.length; i++){
            if(!hm.containsKey(a[i])){
               hm.put(a[i], 1);
            }else{
               hm.put(a[i], hm.get(a[i])+1);
    }               
    System.out.println(hm);         
}

Answer 3

I have a solution for count the frequency of elements in a java array

import java.io.BufferedReader;

import java.io.InputStreamReader;

public class ItemCount {

public static void main(String[] args)
{
    try{
            int count=1,index=1;
            BufferedReader  br=new BufferedReader(new InputStreamReader(System.in));
            System.out.print("Enter the Size of array : ");
            int size=Integer.parseInt(br.readLine());
            System.out.print("Enter the Elements of array : ");
            int arr[]=new int[size];

            for(int i=0;i<arr.length;i++)
            {
                System.out.print("arr["+i+"] :  ");
                arr[i]=Integer.parseInt(br.readLine());
            }
            System.out.print("Sorted Array is :");
            SortingArray.sortDescendind(arr);

            for(int i=0;i<arr.length;i++)
            {
                System.out.println("arr["+i+"] :  "+arr[i]);

            }

            for(int i=0;i<arr.length;)
            {
                count=1;
                for(index=i+1;index<arr.length;index++)
                {
                    if(arr[i]==arr[index])
                    {
                        count++;
                    }
                    else{

                        break;
                    }


                }
                System.out.println(""+arr[i] +"----> "+count);
                i+=count;

            }

    }catch(Exception ex)
    {
        ex.printStackTrace();
    }
}

}

/// you can select any sorting method for array---->SortingArray.sortDescendind(arr)