void RotateUp(AVLNode* cur) {
AVLNode* k = cur->parent;
if (k == NULL) {
return;
}
AVLNode* parent = k->parent;
if (k->left == cur) {
k->left = cur->right;
if (k->left) {
k->left->parent = k;
}
cur->right = k;
k->parent = cur;
} else {
k->right = cur->left;
if (k->right) {
k->right->parent = k;
}
cur->left = k;
k->parent = cur;
}
replaceChild(parent, k, cur);
fixHeight(k);
fixHeight(cur);
fixHeight(parent);
fixSize(k);
fixSize(cur);
fixSize(parent);
}
void TreeDB::rotateLeft(TreeNode*& rootQ)
{
//rotates the root to the left
TreeNode* P = rootQ->right;
rootQ->right = P->left;
P->left = rootQ;
//fixes the heights of the changed trees
fixHeight(rootQ);
fixHeight(P);
//re assigns the root pointer (parent)
rootQ = P;
}
void TreeDB::rotateRight(TreeNode*& rootP)
{
//rotates the root to the right
TreeNode* Q = rootP->left;
rootP->left = Q->right;
Q->right = rootP;
//fixes the heights of the changed trees
fixHeight(rootP);
fixHeight(Q);
//re assigns the root pointer (parent)
rootP = Q;
}
void makeBalance(AVLNode* cur) {
AVLNode* prev = NULL;
while (cur != NULL) {
fixHeight(cur);
fixSize(cur);
int leftHeight = getHeight(cur->left);
int rightHeight = getHeight(cur->right);
if (leftHeight - rightHeight == 2) {
int leftLeftHeight = getHeight(cur->left->left);
int leftRightHeight = getHeight(cur->left->right);
if (leftLeftHeight >= leftRightHeight) {
cur = cur->left;
RotateUp(cur);
} else {
cur = cur->left->right;
RotateUp(cur);
RotateUp(cur);
}
} else if (rightHeight - leftHeight == 2) {
int rightLeftHeight = getHeight(cur->right->left);
int rightRightHeight = getHeight(cur->right->right);
if (rightRightHeight >= rightLeftHeight) {
cur = cur->right;
RotateUp(cur);
} else {
cur = cur->right->left;
RotateUp(cur);
RotateUp(cur);
}
}
prev = cur;
cur = cur->parent;
}
root_ = prev;
}
void TreeDB::balance(TreeNode*& root)
{
fixHeight(root);
//by convention, we are right heavy
if(balanceFactor(root) == 2)
{
//if we have a zig-zag form, we must rotate right then left
if(balanceFactor(root->right) < 0)
{
cout << "rebalancing..." << endl;
rotateRight(root->right);
}
//if we have a linked list form, we only need to rotate left,
//if we had a zig zag form, we already rotated right, now left
cout << "rebalancing..." << endl;
rotateLeft(root);
}
else if(balanceFactor(root) == -2) //left heavy
{
//if we have a zig-zag form, we must rotate left then right
if(balanceFactor(root->left) > 0)
{
cout << "rebalancing..." << endl;
rotateLeft(root->left);
}
//if we have a linked list form, we only need to rotate right,
//if we had a zig zag form, we already rotated left, now right
cout << "rebalancing..." << endl;
rotateRight(root);
}
}
