Dynamic Nested for loop using recursion (All Permutations)

Question

I was trying to implement something like this.

I have bunch of lists.

Each list has certain numbers.

A - 1,2,3 B - 4,5 C - 6,7,8 

I want to find all permutations of A, B, C list That is:

1,4,6 1,4,7 1,4,8 1,5,6 1,5,7 1,5,8 2,4,6 and so on... 

I could have done this using for loop, but the number of lists are not static.

So I tried using recursion.

Here is what I tried: Calling :

nested(number_of_lists,0, array list of array, current_permutation); 

And the function:

static void nested(int depth, int index, ArrayList< ArrayList<Integer> > list, ArrayList<Integer> curr) { if(depth==0) { ArrayList <Integer> x = new ArrayList<>(); int i; for( i=0;i<curr.size();i++) { System.out.println(curr.get(i)); x.add(curr.get(i)); } global.add(x); curr.remove(curr.size()-1); } else { for(int i=0;i<list.get(index).size();i++) { curr.add(list.get(index).get(i)); nested(depth-1, index+1, list, curr); if( curr.size()==list.get(index).size()) { curr.remove(curr.size()-1); } if(index==0 &&(curr.size()-1) == i) curr = new ArrayList<>(); } } } 

Global is new array list of array list which had all permutations stored.

But, after two permutations with A, I get wrong answer

1 4 6 1 4 7 1 4 8 1 5 6 1 5 7 1 5 8 2 4 6 2 4 7 2 4 8 2 5 6 2 5 7 2 5 8 2 3 4 6 2 3 7 2 3 8 2 5 6 2 5 7 

and so on..

Where is the code doing wrong. My first two permutations with two elements of A are perfectly fine. Sorry for such a long explanation. Some help would be appreciated.

Answer 1

You appear to be making this more complicated than it actually is. I have managed to correct this just by commenting out some of your lines.

static void nested(int depth, int index, ArrayList< ArrayList<Integer> > list, ArrayList<Integer> curr) { if(depth==0) { ArrayList <Integer> x = new ArrayList<>(); int i; for( i=0;i<curr.size();i++) { System.out.println(curr.get(i)); x.add(curr.get(i)); } global.add(x); //curr.remove(curr.size()-1); } else { for(int i=0;i<list.get(index).size();i++) { curr.add(list.get(index).get(i)); nested(depth-1, index+1, list, curr); //if (curr.size()==list.get(index).size()) //{ curr.remove(curr.size()-1); //} //if(index==0 &&(curr.size()-1) == i) // curr = new ArrayList<>(); } } }