NULL assignment to a structure pointer is not working through function. What to do? - c

Question

I am trying to implement BST deletion. According to algorithm, we can delete a leaf directly. Now I'm assigning NULL to leaf directly and still this node remains as it is.
In the test case I gave tried to delete leaf and it is not working.
Please help!
struct node * delet(long data, struct node* root)
{
int i=1;
struct node *temp = root,*t;
while(temp != 0)
{
if(data < temp->data)
{
i=2*i;
temp = temp->l;
}
else if(data > temp->data)
{
i = (2*i)+1;
temp = temp->r ;
}
else
{
printf("%d\n",i);
break;
}
}
if(temp->l == 0 && temp->r == 0)
{
temp = 0;
return root;
}
else if(temp->l == 0)
{
temp->data = temp->l->data;
temp->l = 0;
}
else if(temp->r == 0)
{
temp->data = temp->r->data;
temp->r = 0;
}
else
{
t = temp;
t = t->r;
while(t->l != 0)
{
t = t->l;
}
temp->data = t->data;
if(t->r != 0)
{
t->data = t->r->data;
t->r = 0;
return root;
}
else
{
t = 0;
return root;
}
}
}

Answer 1

temp = 0; doesn't delete the leaf from the tree, just nulls a local variable.
You want to null some node's l or r in order to remove a node from the tree.
Try keeping the parent as well and once temp points to the leaf, nullify temp's parent r or l.
Same goes for t = 0; later on.
Note David's comment about first releasing this memory..
For example (assuming not deleting the root):
...
if(data < temp->data)
{
i=2*i;
parent = temp;
temp = temp->l;
}
else if(data > temp->data)
{
i = (2*i)+1;
parent = temp;
temp = temp->r ;
}
else
{
printf("%d\n",i);
break;
}
...
if(temp->l == 0 && temp->r == 0)
{
if (parent->l == temp)
parent->l = 0;
else
parent->r = 0;
// Free temp if needed
return root;
}
...
Also note that you have:
else if(temp->l == 0)
{
temp->data = temp->l->data;
Which is a dereference of a null pointer (temp->l is NULL), and the same thing for temp->r == 0 case.
Then you have
temp->l = 0;
but you're already in a temp->l == 0 case, so I don't think this is what you meant.