Combinations

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Combinations {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        char arr[] = {'a', 'b', 'a', 'c'};
//        char arr[] = {'0', '1','2'};
        int r = 3;
        int n = arr.length;
        printCombination(arr, n, r);

    }
    /* arr[]  ---> Input Array
    data[] ---> Temporary array to store current combination
    start & end ---> Staring and Ending indexes in arr[]
    index  ---> Current index in data[]
    r ---> Size of a combination to be printed */
    static void combinationUtil(char arr[], char data[], int start,
                                int end, int index, int r)
    {
        // Current combination is ready to be printed, print it
        if (index == r)
        {
            for (int j=0; j<r; j++)
                System.out.print(data[j]+" ");
            System.out.println("");
            return;
        }

        // replace index with all possible elements. The condition
        // "end-i+1 >= r-index" makes sure that including one element
        // at index will make a combination with remaining elements
        // at remaining positions
        for (int i = start; i <= end && end - i + 1 >= r - index; i++)
        {
            data[index] = arr[i];
            combinationUtil(arr, data, i + 1, end, index + 1, r);
        }
    }

    // The main function that prints all combinations of size r
    // in arr[] of size n. This function mainly uses combinationUtil()
    static void printCombination(char arr[], int n, int r)
    {
        // A temporary array to store all combination one by one
        char data[]=new char[r];

        // Print all combination using temprary array 'data[]'
        combinationUtil(arr, data, 0, n - 1, 0, r);
    }
}