public void combine(char input[], int pos, boolean used[]){
        printArray(input, used);
        for(int i= pos; i < input.length; i++){
            used[i] = true;
            combine(input, i+1, used);
            used[i] = false;
        }
    }
e.g a, b c 
* * *
a * *
a b *
a b c
* b *
* b c
* * c

Idea is to store the index of values in used[] array. So just
like regular combination if used is set print it else print *
src/com/interview/recursion/CombinationWithStar.java