// If node X is a leaf or has only one child, skip to step 5. (node Z will be node X)
// Otherwise, determine node Y by finding the largest node in node X's left sub tree (in-order predecessor) or the smallest in its right sub tree (in-order successor).
// Replace node X with node Y (remember, tree structure doesn't change here, only the values). In this step, node X is essentially deleted when its internal values were overwritten with node Y's.
// Choose node Z to be the old node Y.
// Attach node Z's subtree to its parent (if it has a subtree). If node Z's parent is null, update root. (node Z is currently root)
// Delete node Z.
// Retrace the path back up the tree (starting with node Z's parent) to the root, adjusting the balance factors as needed.
// As with all binary trees, a node's in-order successor is the left-most child of its right subtree, and a node's in-order predecessor is the right-most child of its left subtree.
// In either case, this node will have zero or one children. Delete it according to one of the two simpler cases above.
// Removes one element from the dictionary
bool
AVLDictionary::removeElement(KeyType key)
{
if (debug) {
printf("------------------------------------\n");
printf("removeElement(\"%s\")\n", key);
printf("---------- Before -----------------\n");
printNode("", root, 0);
}
//need to subsitute root with node that comes immediately before or after
// AVLNode *current = (AVLNode*)findNode(key);
AVLNode *current = root;
while (current != NULL) {
if (strcmp(current->key, key) == 0) {
break;
} else if (strcmp(current->key, key) > 0) {
current = current->left;
} else {
current = current->right;
}
}
if (current == NULL) {
return false;
}
AVLNode *parent = NULL;
if (current != root) {
parent = current->parent;
} else { //is root
current->left = current->right->parent;
}
// if(current == parent->right) {
// parent->right = current->right;
// } else {
// parent->left = current->right;
// }
if (current->left == NULL && current->right == NULL) { //no children, just delete?
if (current == parent->right) {
parent->right = NULL;
} else {
parent->left = NULL;
}
delete current;
restructure(parent);
} else if (current->left == NULL) {
if (current == parent->right) {
parent->right = NULL;
parent->right = current->right;
parent->right->height = current->right->height;
delete current;
current = NULL;
restructure(parent);
} else {
parent->left = NULL;
parent->left = current->right;
parent->left->height = current->right->height;
restructure(parent);
delete current;
current = NULL;
}
// restructure(current->right);
} else if (current->right == NULL) {
if (current == parent->right) {
parent->right = NULL;
parent->right = current->left;
parent->right->height = current->left->height;
// current = current->right;
restructure(parent);
delete current;
current = NULL;
} else {
parent->left = NULL;
parent->left = current->left;
parent->left->height = current->left->height;
restructure(parent);
delete current;
current = NULL;
// current = current->right;
}
// delete current;
// restructure(parent);
// parent->left = current->right;
// current = current->right;
// restructure(current);
// restructure(current->left);
} else { //is internal
AVLNode *preorder = current->left;
while (preorder->right != NULL) {
preorder = preorder->right;
}
current->key = preorder->key;
current->data = preorder->data;
current = preorder;
if (current->left == NULL) {
if (current->parent->right == current) {
current->parent->right = current->right;
} else {
current->parent->left = current->right;
}
} else {
if (current->parent->right == current) {
current->parent->right = current->left;
} else {
current->parent->left = current->left;
}
}
restructure(current->parent);
delete current;
}
if (debug) {
printf("---------- After -----------------\n");
printNode("", root, 0);
checkRecursive(root);
}
return true;
}
// Add a record to the dictionary. Returns false if key already exists
bool
AVLDictionary::addRecord( KeyType key, DataType data) {
if ( debug) {
printf("------------------------------------\n");
printf("addRecord(\"%s\",%d)\n", key, (int)data);
printf("---------- Before -----------------\n");
printNode("", root, 0);
}
//find node with that key, if any
//overwrite data if found
AVLNode *current = root;
AVLNode *prev = NULL;
while (current != NULL) {
prev = current;
if (strcmp(key, current->key) == 0) {
// key == current->key) //
//found, overwrite data
current->data = data;
return false;
} else if (strcmp(key, current->key) > 0) {
// (key - current->key > 0)
//key is in right subtree
current = current->right;
} else { //key is in left subtree
current = current->left;
}
} //did not find key in tree, and prev points to parent node where new node will be inserted
AVLNode *newNode = new AVLNode();
newNode->key = strdup(key); //use strdup if key is const char*
newNode->data = data;
newNode->height = 1;
newNode->left = NULL;
newNode->right = NULL;
newNode->parent = prev;
if (prev == NULL) { //tree is empty, assign to root
root = newNode;
nElements++;
return true;
}
if (strcmp(key, prev->key) > 0) { //attach to right
prev->right = newNode;
} else {
prev->left = newNode;
}
//adjust heights of above subtrees, path from inserted node to root
AVLNode *m = newNode->parent;
while (m != NULL) {//go up
//get maxHeight of left and right children
int maxHeight = 0;
if (m->left != NULL) {
maxHeight = m->left->height;
}
if (m->right != NULL && maxHeight < m->right->height) {
maxHeight = m->right->height;
}
//update height of m
m->height = 1 + maxHeight;
m = m->parent;
}
//at this point, the newnode is in place and height has been adjusted for correctness,
//however, may not fulfill AVL tree conditions, because of potential height differences
//in subtrees (ie difference in height of left and right > 1)
//restructure beginning at inserted node
//Find node to insert into
//Node does not exist. Create it.
//Height might not be valid anymore.
//We need to restructure .
if ( debug) {
printf("---------- Before Restructure -----------------\n");
printNode("", root, 0);
}
// Call restructure
restructure(newNode);
if (debug) {
checkRecursive(root);
printf("---------- After Restructure -----------------\n");
printNode("", root, 0);
}
nElements++;
return true;
}
void
AVLDictionary::checkRecursive(AVLNode * node) {
if (node == NULL) {
return;
}
if (node->left!=NULL) {
// Make sure that it is sorted
if ( strcmp(node->key, node->left->key) <= 0) {
fprintf(stderr,
"*** NOT SORTED: parent->key=\"%s\" <= left->key=\"%s\"\n",
node->key, node->left->key);
assert(0);
}
}
if (node->right!=NULL) {
// Make sure that it is sorted
if ( strcmp(node->key, node->right->key) >= 0) {
fprintf(stderr,
"*** NOT SORTED: parent->key=\"%s\" >= right->key=\"%s\"\n",
node->key, node->right->key);
assert(0);
}
}
checkRecursive(node->left);
checkRecursive(node->right);
// Check height
int lHeight = 0;
if (node->left!=0) {
lHeight = node->left->height;
}
int rHeight = 0;
if (node->right!=0) {
rHeight = node->right->height;
}
int diff = lHeight - rHeight;
if (diff<0) {
diff = - diff;
}
if (diff>1) {
fprintf(stderr,
"*** HEIGHT DIFFERENCE > 1: key=\"%s\" lheight=%d rheight=%d\n",
node->key, lHeight, rHeight);
assert(0);
}
// Compute height
int maxHeight = lHeight;
if (maxHeight<rHeight) {
maxHeight = rHeight;
}
if (node->height != maxHeight + 1) {
fprintf(stderr,
"*** WRONGH HEIGHT: key=\"%s\" height=%d should be %d\n",
node->key, node->height, maxHeight + 1);
assert(0);
}
}
//
// Goes over the nodes in the tree to verify that the height and keys
// of the AVL tree are correct. It prints a message and exits if it is not a
// valid AVL tree.
//
void
AVLDictionary::check()
{
checkRecursive(root);
}
// Removes one element from the dictionary
bool
AVLDictionary::removeElement(KeyType key)
{
if (debug)
{
printf("------------------------------------\n");
printf("removeElement(\"%s\")\n", key);
printf("---------- Before -----------------\n");
printNode("", root, 0);
}
AVLNode *node;
node = findNode(key);
if (node == NULL)
{
return false;
}
if (node->left == NULL && node->right == NULL)
{
if ( node == node->parent->left)
{
node->parent->left = NULL;
}
else
{
node->parent->right = NULL;
}
AVLNode *m;
m = node->parent;
while(m != NULL)
{
int maxheight = 0;
if(m->left != NULL)
{
maxheight = m->left->height;
}
if (m->right != NULL && maxheight < m->right->height)
{
maxheight = m->right->height;
}
m->height = maxheight +1;
m = m->parent;
}
restructure(node->parent);
delete node;
}
else if (node->left == NULL)
{
AVLNode temp;
temp.height = node->height;
strcpy((char*)temp.key, node->key);
temp.data = node->data;
node->height = node->right->height;
strcpy((char*)node->key, node->right->key);
node->data = node->right->data;
node->right->height = temp.height;
strcpy((char*)node->right->key, temp.key);
node->right->data = temp.data;
delete node->right;
node->right = NULL;
AVLNode *m = node->parent;
while(m != NULL)
{
int maxheight = 0;
if(m->left != NULL)
{
maxheight = m->left->height;
}
if (m->right != NULL && maxheight < m->right->height)
{
maxheight = m->right->height;
}
m->height = maxheight +1;
m = m->parent;
}
restructure(node);
}
else if (node->right == NULL)
{
AVLNode temp;
temp.height = node->height;
strcpy((char*)temp.key, node->key);
temp.data = node->data;
node->height = node->left->height;
strcpy((char*)node->key, node->left->key);
node->data = node->left->data;
node->left->height = temp.height;
strcpy((char*)node->left->key, temp.key);
node->left->data = temp.data;
delete node->left;
node->left = NULL;
AVLNode *m;
m = node->parent;
while(m != NULL)
{
int maxheight = 0;
if( m->left != NULL)
{
maxheight = m->left->height;
}
if (m->right != NULL && maxheight < m->right->height)
{
maxheight = m->right->height;
}
m->height = maxheight +1;
m = m->parent;
}
restructure(node);
}
else
{
AVLNode *replacement;
replacement = node->left;
if (replacement->right == NULL)
{
replacement = node->right;
while(replacement->left != NULL)
{
replacement = replacement->left;
}
}
else
{
while (replacement->right != NULL)
{
replacement = replacement->right;
}
}
AVLNode temp;
temp.height = node->height;
strcpy((char*)temp.key, node->key);
temp.data = node->data;
node->height = replacement->height;
strcpy((char*)node->key, replacement->key);
node->data = replacement->data;
replacement->height = temp.height;
strcpy((char*)replacement->key, temp.key);
replacement->data = temp.data;
AVLNode *n;
n = replacement->parent;
if (n != NULL)
{
if (replacement == n->left)
{
n->left = NULL;
delete replacement;
}
else
{
n->right = NULL;
delete replacement;
}
AVLNode *m = n;
while(m != NULL)
{
int maxheight = 0;
if(m->left != NULL)
{
maxheight = m->left->height;
}
if (m->right != NULL && maxheight < m->right->height)
{
maxheight = m->right->height;
}
m->height = maxheight +1;
m = m->parent;
}
restructure(n);
}
}
nElements--;
if (debug)
{
printf("---------- After -----------------\n");
printNode("", root, 0);
checkRecursive(root);
}
return true;
}
// Add a record to the dictionary. Returns false if key already exists
bool
AVLDictionary::addRecord( KeyType key, DataType record)
{
if (debug)
{
printf("------------------------------------\n");
printf("addRecord(\"%s\",%d)\n", key, record);
printf("---------- Before -----------------\n");
printNode("", root, 0);
}
AVLNode *n;
n = new AVLNode();
n->key = key;
n->data = record;
n->height = 1;
n->left = NULL;
n->right = NULL;
n->parent = NULL;
if(root == NULL)
{
root = n;
nElements++;
return true;
}
AVLNode *curr;
curr = root;
AVLNode *prev;
prev = NULL;
while(curr != NULL)
{
prev = curr;
if (strcmp(key, curr->key) < 0)
{
curr = curr->left;
}
else if (strcmp(key, curr->key) > 0)
{
curr = curr->right;
}
else
{
curr->data = record;
return false;
}
}
if (strcmp(key, prev->key) < 0)
{
prev->left = n;
}
else
{
prev->right = n;
}
n->parent = prev;
AVLNode *m;
m = n->parent;
while(m != NULL)
{
int maxheight = 0;
if(m->left != NULL)
maxheight = m->left->height;
if(m->right != NULL && maxheight < m->right->height)
maxheight = m->right->height;
m->height = 1+maxheight;
m = m->parent;
}
if (debug)
{
printf("---------- Before Restructure -----------------\n");
printNode("", root, 0);
}
restructure(n);
if (debug)
{
checkRecursive(root);
printf("---------- After Restructure -----------------\n");
printNode("", root, 0);
}
nElements++;
return true;
}