/*
* Copyright (c) 2007 Vojtech Mencl
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* - The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/** @addtogroup genericadt
* @{
*/
/**
* @file
* @brief AVL tree implementation.
*
* This file implements AVL tree type and operations.
*
* Implemented AVL tree has the following properties:
* @li It is a binary search tree with non-unique keys.
* @li Difference of heights of the left and the right subtree of every node is
* one at maximum.
*
* Every node has a pointer to its parent which allows insertion of multiple
* identical keys into the tree.
*
* Be careful when using this tree because of the base atribute which is added
* to every inserted node key. There is no rule in which order nodes with the
* same key are visited.
*/
#include <adt/avl.h>
#include <debug.h>
#define LEFT 0
#define RIGHT 1
/** Search for the first occurence of the given key in an AVL tree.
*
* @param t AVL tree.
* @param key Key to be searched.
*
* @return Pointer to a node or NULL if there is no such key.
*/
avltree_node_t *avltree_search(avltree_t *t, avltree_key_t key)
{
avltree_node_t *p;
/*
* Iteratively descend to the leaf that can contain the searched key.
*/
p = t->root;
while (p != NULL) {
if (p->key > key)
p = p->lft;
else if (p->key < key)
p = p->rgt;
else
return p;
}
return NULL;
}
/** Find the node with the smallest key in an AVL tree.
*
* @param t AVL tree.
*
* @return Pointer to a node or NULL if there is no node in the tree.
*/
avltree_node_t *avltree_find_min(avltree_t *t)
{
avltree_node_t *p = t->root;
/*
* Check whether the tree is empty.
*/
if (!p)
return NULL;
/*
* Iteratively descend to the leftmost leaf in the tree.
*/
while (p->lft != NULL)
p = p->lft;
return p;
}
/** Insert new node into AVL tree.
*
* @param t AVL tree.
* @param newnode New node to be inserted.
*/
void avltree_insert(avltree_t *t, avltree_node_t *newnode)
{
avltree_node_t *par;
avltree_node_t *gpa;
avltree_node_t *top;
avltree_node_t **dpc;
avltree_key_t key;
ASSERT(t);
ASSERT(newnode);
/*
* Creating absolute key.
*/
key = newnode->key + t->base;
/*
* Iteratively descend to the leaf that can contain the new node.
* Last node with non-zero balance in the way to leaf is stored as top -
* it is a place of possible inbalance.
*/
dpc = &t->root;
gpa = NULL;
top = t->root;
while ((par = (*dpc)) != NULL) {
if (par->balance != 0) {
top = par;
}
gpa = par;
dpc = par->key > key ? &par->lft: &par->rgt;
}
/*
* Initialize new node.
*/
newnode->key = key;
newnode->lft = NULL;
newnode->rgt = NULL;
newnode->par = gpa;
newnode->balance = 0;
/*
* Insert first node into the empty tree.
*/
if (t->root == NULL) {
*dpc = newnode;
return;
}
/*
* Insert new node into previously found leaf place.
*/
*dpc = newnode;
/*
* If the tree contains one node - end.
*/
if (top == NULL)
return;
/*
* Store pointer of top's father which points to the node with
* potentially broken balance (top).
*/
if (top->par == NULL) {
dpc = &t->root;
} else {
if (top->par->lft == top)
dpc = &top->par->lft;
else
dpc = &top->par->rgt;
}
/*
* Repair all balances on the way from top node to the newly inserted
* node.
*/
par = top;
while (par != newnode) {
if (par->key > key) {
par->balance--;
par = par->lft;
} else {
par->balance++;
par = par->rgt;
}
}
/*
* To balance the tree, we must check and balance top node.
*/
if (top->balance == -2) {
par = top->lft;
if (par->balance == -1) {
/*
* LL rotation.
*/
top->lft = par->rgt;
if (top->lft != NULL)
top->lft->par = top;
par->par = top->par;
top->par = par;
par->rgt = top;
par->balance = 0;
top->balance = 0;
*dpc = par;
} else {
/*
* LR rotation.
*/
ASSERT(par->balance == 1);
gpa = par->rgt;
par->rgt = gpa->lft;
if (gpa->lft != NULL)
gpa->lft->par = par;
gpa->lft = par;
par->par = gpa;
top->lft = gpa->rgt;
if (gpa->rgt != NULL)
gpa->rgt->par = top;
gpa->rgt = top;
gpa->par = top->par;
top->par = gpa;
if (gpa->balance == -1) {
par->balance = 0;
top->balance = 1;
} else if (gpa->balance == 0) {
par->balance = 0;
top->balance = 0;
} else {
par->balance = -1;
top->balance = 0;
}
gpa->balance = 0;
*dpc = gpa;
}
} else if (top->balance == 2) {
par = top->rgt;
if (par->balance == 1) {
/*
* RR rotation.
*/
top->rgt = par->lft;
if (top->rgt != NULL)
top->rgt->par = top;
par->par = top->par;
top->par = par;
par->lft = top;
par->balance = 0;
top->balance = 0;
*dpc = par;
} else {
/*
* RL rotation.
*/
ASSERT(par->balance == -1);
gpa = par->lft;
par->lft = gpa->rgt;
if (gpa->rgt != NULL)
gpa->rgt->par = par;
gpa->rgt = par;
par->par = gpa;
top->rgt = gpa->lft;
if (gpa->lft != NULL)
gpa->lft->par = top;
gpa->lft = top;
gpa->par = top->par;
top->par = gpa;
if (gpa->balance == 1) {
par->balance = 0;
top->balance = -1;
} else if (gpa->balance == 0) {
par->balance = 0;
top->balance = 0;
} else {
par->balance = 1;
top->balance = 0;
}
gpa->balance = 0;
*dpc = gpa;
}
} else {
/*
* Balance is not broken, insertion is finised.
*/
return;
}
}
/** Repair the tree after reparenting node u.
*
* If node u has no parent, mark it as the root of the whole tree. Otherwise
* node v represents stale address of one of the children of node u's parent.
* Replace v with w as node u parent's child (for most uses, u and w will be the
* same).
*
* @param t AVL tree.
* @param u Node whose new parent has a stale child pointer.
* @param v Stale child of node u's new parent.
* @param w New child of node u's new parent.
* @param dir If not NULL, address of the variable where to store information
* about whether w replaced v in the left or the right subtree of
* u's new parent.
* @param ro Read only operation; do not modify any tree pointers. This is
* useful for tracking direction via the dir pointer.
*
* @return Zero if w became the new root of the tree, otherwise return
* non-zero.
*/
static int
repair(avltree_t *t, avltree_node_t *u, avltree_node_t *v, avltree_node_t *w,
int *dir, int ro)
{
if (u->par == NULL) {
if (!ro)
t->root = w;
return 0;
} else {
if (u->par->lft == v) {
if (!ro)
u->par->lft = w;
if (dir)
*dir = LEFT;
} else {
ASSERT(u->par->rgt == v);
if (!ro)
u->par->rgt = w;
if (dir)
*dir = RIGHT;
}
}
return 1;
}
#define REBALANCE(DIR1, DIR2, SIGN) \
if (cur->balance == -1 * SIGN) { \
par->balance = 0; \
gpa->balance = 1 * SIGN; \
if (gpa->DIR1) \
gpa->DIR1->par = gpa; \
par->DIR2->par = par; \
} else if (cur->balance == 0) { \
par->balance = 0; \
gpa->balance = 0; \
if (gpa->DIR1) \
gpa->DIR1->par = gpa; \
if (par->DIR2) \
par->DIR2->par = par; \
} else { \
par->balance = -1 * SIGN; \
gpa->balance = 0; \
if (par->DIR2) \
par->DIR2->par = par; \
gpa->DIR1->par = gpa; \
} \
cur->balance = 0;
#define REBALANCE_LR() REBALANCE(lft, rgt, 1)
#define REBALANCE_RL() REBALANCE(rgt, lft, -1)
/** Delete a node from the AVL tree.
*
* Because multiple identical keys are allowed, the parent pointers are
* essential during deletion.
*
* @param t AVL tree structure.
* @param node Address of the node which will be deleted.
*/
void avltree_delete(avltree_t *t, avltree_node_t *node)
{
avltree_node_t *cur;
avltree_node_t *par;
avltree_node_t *gpa;
int dir;
ASSERT(t);
ASSERT(node);
if (node->lft == NULL) {
if (node->rgt) {
/*
* Replace the node with its only right son.
*
* Balance of the right son will be repaired in the
* balancing cycle.
*/
cur = node->rgt;
cur->par = node->par;
gpa = cur;
dir = RIGHT;
cur->balance = node->balance;
} else {
if (node->par == NULL) {
/*
* The tree has only one node - it will become
* an empty tree and the balancing can end.
*/
t->root = NULL;
return;
}
/*
* The node has no child, it will be deleted with no
* substitution.
*/
gpa = node->par;
cur = NULL;
dir = (gpa->lft == node) ? LEFT: RIGHT;
}
} else {
/*
* The node has the left son. Find a node with the smallest key
* in the left subtree and replace the deleted node with that
* node.
*/
for (cur = node->lft; cur->rgt != NULL; cur = cur->rgt)
;
if (cur != node->lft) {
/*
* The rightmost node of the deleted node's left subtree
* was found. Replace the deleted node with this node.
* Cutting off of the found node has two cases that
* depend on its left son.
*/
if (cur->lft) {
/*
* The found node has a left son.
*/
gpa = cur->lft;
gpa->par = cur->par;
dir = LEFT;
gpa->balance = cur->balance;
} else {
dir = RIGHT;
gpa = cur->par;
}
cur->par->rgt = cur->lft;
cur->lft = node->lft;
cur->lft->par = cur;
} else {
/*
* The left son of the node hasn't got a right son. The
* left son will take the deleted node's place.
*/
dir = LEFT;
gpa = cur;
}
if (node->rgt)
node->rgt->par = cur;
cur->rgt = node->rgt;
cur->balance = node->balance;
cur->par = node->par;
}
/*
* Repair the parent node's pointer which pointed previously to the
* deleted node.
*/
(void) repair(t, node, node, cur, NULL, false);
/*
* Repair cycle which repairs balances of nodes on the way from from the
* cut-off node up to the root.
*/
for (;;) {
if (dir == LEFT) {
/*
* Deletion was made in the left subtree.
*/
gpa->balance++;
if (gpa->balance == 1) {
/*
* Stop balancing, the tree is balanced.
*/
break;
} else if (gpa->balance == 2) {
/*
* Bad balance, heights of left and right
* subtrees differ more than by one.
*/
par = gpa->rgt;
if (par->balance == -1) {
/*
* RL rotation.
*/
cur = par->lft;
par->lft = cur->rgt;
cur->rgt = par;
gpa->rgt = cur->lft;
cur->lft = gpa;
/*
* Repair balances and paternity of
* children, depending on the balance
* factor of the grand child (cur).
*/
REBALANCE_RL();
/*
* Repair paternity.
*/
cur->par = gpa->par;
gpa->par = cur;
par->par = cur;
if (!repair(t, cur, gpa, cur, &dir,
false))
break;
gpa = cur->par;
} else {
/*
* RR rotation.
*/
gpa->rgt = par->lft;
if (par->lft)
par->lft->par = gpa;
par->lft = gpa;
/*
* Repair paternity.
*/
par->par = gpa->par;
gpa->par = par;
if (par->balance == 0) {
/*
* The right child of the
* balanced node is balanced,
* after RR rotation is done,
* the whole tree will be
* balanced.
*/
par->balance = -1;
gpa->balance = 1;
(void) repair(t, par, gpa, par,
NULL, false);
break;
} else {
par->balance = 0;
gpa->balance = 0;
if (!repair(t, par, gpa, par,
&dir, false))
break;
}
gpa = par->par;
}
} else {
/*
* Repair the pointer which pointed to the
* balanced node. If it was root then balancing
* is finished else continue with the next
* iteration (parent node).
*/
if (!repair(t, gpa, gpa, NULL, &dir, true))
break;
gpa = gpa->par;
}
} else {
/*
* Deletion was made in the right subtree.
*/
gpa->balance--;
if (gpa->balance == -1) {
/*
* Stop balancing, the tree is balanced.
*/
break;
} else if (gpa->balance == -2) {
/*
* Bad balance, heights of left and right
* subtrees differ more than by one.
*/
par = gpa->lft;
if (par->balance == 1) {
/*
* LR rotation.
*/
cur = par->rgt;
par->rgt = cur->lft;
cur->lft = par;
gpa->lft = cur->rgt;
cur->rgt = gpa;
/*
* Repair balances and paternity of
* children, depending on the balance
* factor of the grand child (cur).
*/
REBALANCE_LR();
/*
* Repair paternity.
*/
cur->par = gpa->par;
gpa->par = cur;
par->par = cur;
if (!repair(t, cur, gpa, cur, &dir,
false))
break;
gpa = cur->par;
} else {
/*
* LL rotation.
*/
gpa->lft = par->rgt;
if (par->rgt)
par->rgt->par = gpa;
par->rgt = gpa;
/*
* Repair paternity.
*/
par->par = gpa->par;
gpa->par = par;
if (par->balance == 0) {
/*
* The left child of the
* balanced node is balanced,
* after LL rotation is done,
* the whole tree will be
* balanced.
*/
par->balance = 1;
gpa->balance = -1;
(void) repair(t, par, gpa, par,
NULL, false);
break;
} else {
par->balance = 0;
gpa->balance = 0;
if (!repair(t, par, gpa, par,
&dir, false))
break;
}
gpa = par->par;
}
} else {
/*
* Repair the pointer which pointed to the
* balanced node. If it was root then balancing
* is finished. Otherwise continue with the next
* iteration (parent node).
*/
if (!repair(t, gpa, gpa, NULL, &dir, true))
break;
gpa = gpa->par;
}
}
}
}
/** Delete a node with the smallest key from the AVL tree.
*
* @param t AVL tree structure.
*/
bool avltree_delete_min(avltree_t *t)
{
avltree_node_t *node;
/*
* Start searching for the smallest key in the tree starting in the root
* node and continue in cycle to the leftmost node in the tree (which
* must have the smallest key).
*/
node = t->root;
if (!node)
return false;
while (node->lft != NULL)
node = node->lft;
avltree_delete(t, node);
return true;
}
static void _avltree_walk(avltree_node_t *node, avltree_walker_t walker)
{
if (node->lft)
_avltree_walk(node->lft, walker);
walker(node);
if (node->rgt)
_avltree_walk(node->rgt, walker);
}
/** Walk the AVL tree and apply the walker function on each visited node.
*
* @param t AVL tree to be walked.
* @param walker Walker function that will be called on each visited
* node.
*/
void avltree_walk(avltree_t *t, avltree_walker_t walker)
{
_avltree_walk(t->root, walker);
}
/** @}
*/