private void combinationUtil(int arr[],int k, int pos,int result[],int start){
        if(pos == k){
            for(int i=0; i < k; i++){
                System.out.print(result[i] + " ");
            }
            System.out.print("\n");
            return;
        }
        for(int i=start; i < arr.length; i++){
            result[pos] = arr[i];
            combinationUtil(arr,k,pos+1,result,i+1);
        }
    }
http://www.geeksforgeeks.org/print-all-possible-combinations-of-r-elements-in-a-given-array-of-size-n/
src/com/interview/recursion/CombinationOfSizeK.java