插入3D arraylist

Question

I have created 3D ArrayList. I know initialization is done using this code

ArrayList<ArrayList<ArrayList>> ll=new ArrayList<ArrayList<ArrayList>>();  
for(int j=0;j<n;j++){
    ll.add(new ArrayList(new ArrayList()));
}

But I dont know how insert values in it. I am familiar with 2D arraylist in which inserting value b at a index is done using

ll.get(a).add(b);

but I dont know how to insert value into 3D arrayList.

I am solving question http://www.spoj.com/problems/BENEFACT/
in which I think longest distance in tree is the answer. I used 3D ArrayList here, 2dimension to store connection of places and 3rd dimension to store distance

Is this correct approach? Is Any other approach possible in which solution is obtained easier than using 3d ArrayList?

Answer 1

I think if you want to access an object at index i,j,k you can do it by

ll.get(i).get(j).get(k)

Or

ll.get(i).get(j).add(k,newObject)

Answer 2

Depending on your need, you probably don't want that. I didn't read the full description of the problem to solve (the link), but you just need 6 points in 3D space.

I'd suggest creating a Point3D class with x , y , and z , and then just a simple List<Point3D> .