/* Remove an element a from the AVL tree t
* returns -1 if the depth of the tree has shrunk
* Warning: if the element is not present in the tree,
* returns 0 as if it had been removed succesfully.
*/
int avl_remove(avl_tree* t, avl* a) {
int b;
if (t->root == a)
return avl_removeroot(t);
b = t->compar(t->root, a);
if (b >= 0) {
/* remove from the left subtree */
int ch;
avl_tree left_subtree;
if ((left_subtree.root = t->root->left)) {
left_subtree.compar = t->compar;
ch = avl_remove(&left_subtree, a);
t->root->left = left_subtree.root;
if (ch) {
switch (t->root->balance++) {
case -1:
return -1;
case 0:
return 0;
}
switch (t->root->right->balance) {
case 0:
avl_swl(&(t->root));
t->root->balance = -1;
t->root->left->balance = 1;
return 0;
case 1:
avl_swl(&(t->root));
t->root->balance = 0;
t->root->left->balance = 0;
return -1;
}
avl_swr(&(t->root->right));
avl_swl(&(t->root));
avl_nasty(t->root);
return -1;
}
}
}
if (b <= 0) {
/* remove from the right subtree */
int ch;
avl_tree right_subtree;
if ((right_subtree.root = t->root->right)) {
right_subtree.compar = t->compar;
ch = avl_remove(&right_subtree, a);
t->root->right = right_subtree.root;
if (ch) {
switch (t->root->balance--) {
case 1:
return -1;
case 0:
return 0;
}
switch (t->root->left->balance) {
case 0:
avl_swr(&(t->root));
t->root->balance = 1;
t->root->right->balance = -1;
return 0;
case -1:
avl_swr(&(t->root));
t->root->balance = 0;
t->root->right->balance = 0;
return -1;
}
avl_swl(&(t->root->left));
avl_swr(&(t->root));
avl_nasty(t->root);
return -1;
}
}
}
return 0;
}
// Remove an already-selected node n from the AVL tree t.
// Returns True if the depth of the tree has shrunk.
static Bool avl_remove(AvlTree* t, AvlNode* n)
{
Bool ch;
Word cmpres = cmp_key_root(t, n);
if (cmpres < 0) {
AvlTree left_subtree;
// Remove from the left subtree
vg_assert(t->root->left);
// Only need to set the used fields in the subtree.
left_subtree.root = t->root->left;
left_subtree.cmp = t->cmp;
left_subtree.keyOff = t->keyOff;
ch = avl_remove(&left_subtree, n);
t->root->left = left_subtree.root;
if (ch) {
switch (t->root->balance++) {
case -1: return True;
case 0: return False;
}
switch (t->root->right->balance) {
case 0:
avl_swl(&(t->root));
t->root->balance = -1;
t->root->left->balance = 1;
return False;
case 1:
avl_swl(&(t->root));
t->root->balance = 0;
t->root->left->balance = 0;
return True;
}
avl_swr(&(t->root->right));
avl_swl(&(t->root));
avl_nasty(t->root);
return True;
} else {
return False;
}
} else if (cmpres > 0) {
// Remove from the right subtree
AvlTree right_subtree;
vg_assert(t->root->right);
// Only need to set the used fields in the subtree.
right_subtree.root = t->root->right;
right_subtree.cmp = t->cmp;
right_subtree.keyOff = t->keyOff;
ch = avl_remove(&right_subtree, n);
t->root->right = right_subtree.root;
if (ch) {
switch (t->root->balance--) {
case 1: return True;
case 0: return False;
}
switch (t->root->left->balance) {
case 0:
avl_swr(&(t->root));
t->root->balance = 1;
t->root->right->balance = -1;
return False;
case -1:
avl_swr(&(t->root));
t->root->balance = 0;
t->root->right->balance = 0;
return True;
}
avl_swl(&(t->root->left));
avl_swr(&(t->root));
avl_nasty(t->root);
return True;
} else {
return False;
}
} else {
// Found the node to be removed.
vg_assert(t->root == n);
return avl_removeroot(t);
}
}
