Question

I’m currently working on an applet that displays a heap as values are added and removed. I’m implementing the heaps as tree of integers – IntTrees. I’m writing the code for skew heaps, and the ‘add’ method is giving me some trouble. The add method usually works, but once in a while it causes a stack overflow error when a value is added, and I can’t seem to figure out why.

Here’s the code I have written for the add method

‘t’ is an instance variable – the heap itself.

 // adds value to heap
 public void add(int value) {

IntTree smallTree = new IntTree(value, empty(), empty());

 if (t == null) {
  t = smallTree;
 } else {
  t = merge(t, smallTree);
  }
}

public IntTree merge(IntTree left, IntTree right) {

if (isEmpty(left)) return right;
if (isEmpty(right)) return left;

int leftVal = left.value();
int rightVal = right.value();
IntTree result;

if (rightVal <= leftVal) {
  result = merge(right,left);
} else {
  result = left;

  if (result.isEmpty(left)) {
    result.setLeft(right);
  } else {
    IntTree temp = result.right();
    result.setRight(result.left());
    result.setLeft(merge(temp,right));
  }
}

    return result;
  } 

Is there something in this code that would cause a stack overflow error, or is the problem perhaps elsewhere in the program? Thanks!

Answer 1

Take a look at this snippet

if (rightVal <= leftVal) {
  result = merge(right,left);

What happens when rightVal == leftVal?