I have problem with the remove method in a RB tree. There is a NullPointerException at x.parent=y.parent. The problem is definitely x=null, and if I use this x in method DeleteFixUp there is NullPointerException too. Where do I have a mistake?
Element delete(Element DeleteNode)
{
Element x=null;
Element y=null;
if((DeleteNode.left==null)||(DeleteNode.right==null))
y=DeleteNode;
else
y=Succesor(DeleteNode,root);
if (y.left != null)
x=y.left;
else
x=y.right;
x.parent=y.parent;
if (y.parent == null)
root = x;
else
if (y == y.parent.left)
y.parent.left = x;
else
y.parent.right = x;
if (y != DeleteNode)
DeleteNode.value = y.value;
if(!isRed(y))
{ DeleteFixUp(x);}
return y;
}
And here is Successor method:
Element Succesor(Element x, Element root)
{
if( x.right != null )
{ x=FindMin(x.right);
return x;
}
Element succ = null;
while (root != null)
{
if (_comparator.compare(x.value,root.value)==-1)
{
succ = root;
root = root.left;
}
else if ((_comparator.compare(x.value,root.value)==1))
root = root.right;
else
break;
}
return succ;
}
Okey, I have solved this problem, but I have another one. I add to my code:
Element delete(Element DeleteNode)
{
Element x=null;
Element y=null;
if((DeleteNode.left==null)||(DeleteNode.right==null))
y=DeleteNode;
else
y=Succesor(DeleteNode,root);
if (y.left != null)
x=y.left;
else
x=y.right;
//added to code
if (x == null)
{x = new Element(null);
x.kolor=0;
}
x.parent=y.parent;
if (y.parent == null)
root = x;
else
if (y == y.parent.left)
y.parent.left = x;
else
y.parent.right = x;
if (y != DeleteNode)
DeleteNode.value = y.value;
if(!isRed(y))
{ DeleteFixUp(x);}
return y;
}
Now, I have a question, how to remove this x.value=null, after delete?
