/*
* rebalance a sub-tree whose right branch has been reduced by one level
* because of deletion
*/
AVLNode *
AVL_RebalanceShorterRight(AVLNode * self, int *height_changed)
{
#ifndef __CXC__
AVLNode *p = self;
#else
AVLNode *p;
p = self;
#endif
switch (p->balance) {
case Equal:
p->balance = LeftHigh;
*height_changed = 0;
break;
case RightHigh:
/* taller (right) subtree was shortened */
p->balance = Equal;
break;
case LeftHigh:
{
/*
* shorter (right) sub-tree was shortened, violating
* AVL rules
*/
AVLNode *q;
q = p->left;
switch (q->balance) {
case Equal:
*height_changed = 0;
q->balance = RightHigh;
p = AVL_RotateRight(p);
break;
case LeftHigh:
p->balance = q->balance = Equal;
p = AVL_RotateRight(p);
break;
case RightHigh:
p = AVL_DoubleRotateRight(p);
break;
}
break;
}
}
return p;
}
treenode *AVL_LeftBalance(treenode * r)
{
treenode *x;
treenode *w;
x = r->Lchild;
switch (x->bf) {
case LH:
r->bf = EH;
x->bf = EH;
r = AVL_RotateRight(r);
break;
#ifdef AVL_DEBUG
case EH:
Error(6);
break;
#endif
case RH:
w = x->Rchild;
switch (w->bf) {
case EH:
r->bf = EH;
x->bf = EH;
break;
case RH:
r->bf = EH;
x->bf = LH;
break;
case LH:
r->bf = RH;
x->bf = EH;
break;
}
w->bf = EH;
x = AVL_RotateLeft(x);
r->Lchild = x;
r = AVL_RotateRight(r);
}
return r;
}
/*
* Rebalance sub-tree whose left branch has become heavier because of
* insertion
*/
AVLNode *
AVL_RebalanceHeavierLeft(AVLNode * self, int *height_changed)
{
#ifndef __CXC__
AVLNode *root = self;
#else
AVLNode *root;
root = self;
#endif
/* left-subtree has grown by one level */
switch (root->balance) {
case RightHigh:
root->balance = Equal;
*height_changed = 0;
break;
case Equal:
root->balance = LeftHigh;
break;
case LeftHigh:
{
#ifndef __CXC__
AVLNode *lf = self->left;
#else
AVLNode *lf;
lf = self->left;
#endif
switch (lf->balance) {
case LeftHigh:
self->balance = Equal;
lf->balance = Equal;
root = AVL_RotateRight(self);
break;
case RightHigh:
root = AVL_DoubleRotateRight(self);
break;
default:
break;
}
*height_changed = 0;
break;
}
}
return root;
}
/* doubly rotate sub-tree and return new root (change balance as needed) */
AVLNode *
AVL_DoubleRotateLeft(AVLNode * self)
{
#ifndef __CXC__
AVLNode *rt = self->right;
AVLNode *lf = rt->left;
AVLNode *root;
#else
AVLNode *rt;
AVLNode *lf;
AVLNode *root;
rt = self->right;
lf = rt->left;
#endif
switch (lf->balance) {
case RightHigh:
self->balance = LeftHigh;
rt->balance = Equal;
break;
case Equal:
self->balance = rt->balance = Equal;
break;
case LeftHigh:
self->balance = Equal;
rt->balance = RightHigh;
break;
}
lf->balance = Equal;
AVL_SetRight(self, AVL_RotateRight(rt));
root = AVL_RotateLeft(self);
return root;
}