N while loops into recursion

Hi all,

so, i have this list of elements, and what i want to do, is firstly read a number from console,which tells the program how many elements must be excluded from the list, and then print all possible combinations of this modified element list (ElementList.lenght - n). As an example, if i have a list, that contains 7 elements, and user types into the console 2, that means that the program needs to print out all possible combinations of elements, which can be made out of any 5 elements contained in that same list.

I think that it is possible to make it with nested while loops (i wasn't able though), but only for a fixed user input number, so thats why i need to use recursion.

Ty in advance!

Quote:

---

Originally Posted by Claymz

Hi all,

so, i have this list of elements, and what i want to do, is firstly read a number from console,which tells the program how many elements must be excluded from the list, and then print all possible combinations of this modified element list (ElementList.lenght - n). As an example, if i have a list, that contains 7 elements, and user types into the console 2, that means that the program needs to print out all possible combinations of elements, which can be made out of any 5 elements contained in that same list.

I think that it is possible to make it with nested while loops (i wasn't able though), but only for a fixed user input number, so thats why i need to use recursion.

Ty in advance!

---

You don't need recursion: suppose you have n elements and you want to find all combinations m <= n. e.g. n == 3 and m == 2, so have the element 0, 1 and 2 and you want to list the combinations 01, 02, 12. Given a current combination you can find the next one with this method:

Code:

---

boolean next(int[] comb, int n) {
        for (int i= comb.length; --i >= 0;) {
                if (++comb[i] <= n-(comb.length-i)) {
                        for (; ++i < comb.length; )
                                comb[i]= comb[i-1]+1;
                        return true;
                }
        }
        return false;
}

---

The method returns true if a next combination could be found and false otherwise. Simply apply this method in a loop while it returns true.

kind regards,

Jos