Frequencies of Limited Range Array Elements Java

PROGRAM TO COUNT FREQUENCIES OF ALL ELEMENTS OF ALL ELEMENTS IN ARRAY 




class CountFrequency

{

    // Function to find counts of all elements present in

    // arr[0..n-1]. The array elements must be range from

    // 1 to n

    void printfrequency(int arr[], int n)

    {

        // Subtract 1 from every element so that the elements

        // become in range from 0 to n-1

        for (int j = 0; j < n; j++)

            arr[j] = arr[j] - 1;

 

        // Use every element arr[i] as index and add 'n' to

        // element present at arr[i]%n to keep track of count of

        // occurrences of arr[i]

        for (int i = 0; i < n; i++)

            arr[arr[i] % n] = arr[arr[i] % n] + n;

 

        // To print counts, simply print the number of times n

        // was added at index corresponding to every element

        for (int i = 0; i < n; i++)

            System.out.println(i + 1 + "->" + arr[i] / n);

    }

 

    // Driver program to test above functions

    public static void main(String[] args)

    {

        CountFrequency count = new CountFrequency();

        int arr[] = {2, 3, 3, 2, 5};

        int n = arr.length;

        count.printfrequency(arr, n);

    }

}







OUTPUT

1 ->  0
2 ->  2
3 ->  2
4 ->  0
5 ->  1

CREDITS: https://www.geeksforgeeks.org/count-frequencies-elements-array-o1-extra-space-time/