Question

I get an OutOfMemoryError: Java heap space adding an array of sorted elements to array implementation of a binary search tree. I can add arrays of random Integers fine but when I try adding a sorted array I run into this problem. The root of tree is being set to the smallest or largest element of the sorted array, so when you add the rest of the elements I end up with a extremely unbalanced tree which eats up my memory. Any help on this is much appreciated.

Exception in thread “main” java.lang.OutOfMemoryError: Java heap space
at bst.ArrayBinarySearchTree.resize(ArrayBinarySearchTree.java:386)
at bst.ArrayBinarySearchTree.addElement(ArrayBinarySearchTree.java:26)
at bst.Experiment.main(Experiment.java:90)

    public void addElement(T element) {
    if(isEmpty()){
    count++;
    array[1] = element;
    }else{

         int current = 1;
         boolean added = false;

         while (!added) {
             if(current > (array.length-(array.length*.9))){
                    resize();
                }
            if (element.compareTo(array[current]) < 0){
               if (array[current*2] == null) {
                  array[current*2]=element;
                  added = true;
               } else
                  current = current*2;
            } else{
               if (array[current*2+1] == null) {
                  array[current*2+1]=element;
                  added = true;
               } else
                  current = current*2+1;
            }
         } //while
    }
    count++;
}

    private void resize(){
    T[] temp = (T[])(new Comparable[2*array.length-(array.length/4)]);
    for(int i=0; i<array.length; i++)
        temp[i] = array[i];
    array = temp;
}

Answer 1

well, you will get an unbalanced tree if you dont have balancing in your tree, such as AVL or red black trees. If you are just building a binary search tree without balancing, it s possible that you get a out of memory exception.

I would recommend you to try it with smaller array, to see if you still get a outofmemory exception. if yes, you have a flaw in your code.

I have a binary search tree in c#, take a look at it. Usually you want to use Nodes instead of using an array to represent a binary search tree. As far as i see, you are using a technique which is usually used for heap data structure for heap sort.