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/*
* ANSI C Library for maintainance of AVL Balanced Trees
*
* ref.:
* G. M. Adelson-Velskij & E. M. Landis
* Doklady Akad. Nauk SSSR 146 (1962), 263-266
*
* see also:
* D. E. Knuth: The Art of Computer Programming Vol.3 (Sorting and Searching)
*
* (C) 2000 Daniel Nagy, Budapest University of Technology and Economics
* Released under GNU General Public License (GPL) version 2
*
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "avl.h"
/* Private methods */
int _avl_removeroot(avl_tree* t);
/* Swing to the left
* Warning: no balance maintainance
*/
void avl_swl(avl** root) {
avl* a = *root;
avl* b = a->right;
*root = b;
a->right = b->left;
b->left = a;
}
/* Swing to the right
* Warning: no balance maintainance
*/
void avl_swr(avl** root) {
avl* a = *root;
avl* b = a->left;
*root = b;
a->left = b->right;
b->right = a;
}
/* Balance maintainance after especially nasty swings
*/
void avl_nasty(avl* root) {
switch (root->balance) {
case -1:
root->left->balance = 0;
root->right->balance = 1;
break;
case 1:
root->left->balance = -1;
root->right->balance = 0;
break;
case 0:
root->left->balance = 0;
root->right->balance = 0;
}
root->balance = 0;
}
/* Public methods */
/* Insert element a into the AVL tree t
* returns 1 if the depth of the tree has grown
* Warning: do not insert elements already present
*/
int _avl_insert(avl_tree* t, avl* a) {
/* initialize */
a->left = 0;
a->right = 0;
a->balance = 0;
/* insert into an empty tree */
if (!t->root) {
t->root = a;
return 1;
}
if (t->compar(t->root, a) > 0) {
/* insert into the left subtree */
if (t->root->left) {
avl_tree left_subtree;
left_subtree.root = t->root->left;
left_subtree.compar = t->compar;
if (_avl_insert(&left_subtree, a)) {
switch (t->root->balance--) {
case 1:
return 0;
case 0:
return 1;
}
if (t->root->left->balance < 0) {
avl_swr(&(t->root));
t->root->balance = 0;
t->root->right->balance = 0;
} else {
avl_swl(&(t->root->left));
avl_swr(&(t->root));
avl_nasty(t->root);
}
} else
t->root->left = left_subtree.root;
return 0;
} else {
t->root->left = a;
if (t->root->balance--)
return 0;
return 1;
}
} else {
/* insert into the right subtree */
if (t->root->right) {
avl_tree right_subtree;
right_subtree.root = t->root->right;
right_subtree.compar = t->compar;
if (_avl_insert(&right_subtree, a)) {
switch (t->root->balance++) {
case -1:
return 0;
case 0:
return 1;
}
if (t->root->right->balance > 0) {
avl_swl(&(t->root));
t->root->balance = 0;
t->root->left->balance = 0;
} else {
avl_swr(&(t->root->right));
avl_swl(&(t->root));
avl_nasty(t->root);
}
} else
t->root->right = right_subtree.root;
return 0;
} else {
t->root->right = a;
if (t->root->balance++)
return 0;
return 1;
}
}
}
int avl_insert(avl_tree* t, avl* a) {
#ifdef AVL_LOCK_WITH_MUTEX
pthread_mutex_lock(&t->mutex);
#else
pthread_rwlock_wrlock(&t->rwlock);
#endif
int ret = _avl_insert(t, a);
#ifdef AVL_LOCK_WITH_MUTEX
pthread_mutex_unlock(&t->mutex);
#else
pthread_rwlock_unlock(&t->rwlock);
#endif
return ret;
}
/* 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(&<
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