find the frequency of elements in a java array

Solution 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);
    }
}

Solution 2:

In Java 8 you can do this

Map<Integer, Long> freq = Arrays.stream(array).boxed().
                collect(Collectors.groupingBy(Integer::intValue, Collectors.counting()));

Solution 3:

You have to do a few things:

1. Define an upper and lower bound for your range of numbers.
2. Establish a convenient object/data structure to store occurrences of these numbers.
3. Iterate through the passed-in array and count all occurrences of each number, storing the result in the convenient object/data structure.

If this is done in a simple manner, it could be only a matter of reading the elements from the passed-in array and printing out the final result.

Solution 4:

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);         
}

Solution 5:

import java.util.*;
class Findfreqarray
{
    public static void main(String args[])
    {
        int t, i, j, len, count=0;
        Scanner in = new Scanner(System.in);
        System.out.println("Enter number of elements to insert in an array: ");
        len = in.nextInt();
        int[] arr = new int[len];
        System.out.println("Enter elements to insert in an array: ");
        for(i=0;i<len;i++)
        {
            t = in.nextInt();
            arr[i] = t;
        }
        System.out.println("\n");
        for(i=0;i<len;i++)
        {
            count=1;
            for(j=i+1;j<=len-1;j++)
            {
                if(arr[i]==arr[j] && arr[i]!='\0')
                {
                    count++;
                    arr[j] = '\0';
                }
            }
            if(arr[i]!='\0')
            {
                System.out.println(arr[i] + " is " + count + " times.\n");
            }
        }        
    }
}