/*
* After an insertion, possibly rebalance the tree so that the left and right
* node heights don't differ by more than 1.
* May update *node.
*/
static void
avlAdjustBalance(avl_tree *tree, avl_node **node)
{
avl_node *current = *node;
int b = avlBalance(current) / 2;
if (b != 0)
{
int dir = (1 - b) / 2;
if (avlBalance(current->children[dir]) == -b)
avlRotate(¤t->children[dir], !dir);
current = avlRotate(node, dir);
}
if (current != tree->end)
avlUpdateHeight(current);
}
//Recursively prints the tree - used for debugging
void printTree( AvlNode *node, int depth, int left ) {
//base case
if( node == NULL ) return;
//print space so you can tell how deep this node is
int i;
for( i = 0; i < depth; i++ ) {
printf( " " );
}
//print whether this was a left or right subchild
printf( left ? "L: " : "R: " );
//print data for the node
printf( "%s height:%d balance:%d\n", node->data, node->height, avlBalance( node ) );
//recurse on children
printTree( node->left, depth + 1, 1 );
printTree( node->right, depth + 1, 0 );
}
//Finds the right spot for the word in question
//and adds a node to the tree if necessary.
//Returns the new tree from this node down.
//Also sets the global avlFindAddReturn to
//the word's corresponding node.
AvlNode *avlFindAdd( AvlNode *from, char *newData ) {
//If the current node is null, a new node
//must be created and returned
if( from == NULL ) {
AvlNode *out = avlNew( newData );
avlFindAddReturn = out;
avlFindAddNodeAdded = 1;
return out;
}
//Compare the word we're looking for to the word
//at this node
int comp;
AvlNode *toAdd;
comp = strcmp( newData, from->data );
//Update the left or right subtree to ensure
//it includes a node for this word. If the word
//is in this node, set bstFindAddReturn to this node.
if( comp < 0 ) {
from->left = avlFindAdd( from->left, newData );
} else if( comp > 0 ) {
from->right = avlFindAdd( from->right, newData );
} else {
avlFindAddReturn = from;
}
//If a node was added, some things need to be done.
if( avlFindAddNodeAdded ) {
//Update the height
avlSetHeight( from );
int balance = avlBalance( from );
//If the balance factor at this node is
//2 or -2, a rebalance must be done to
//conform to AVL.
if( balance == -2 ) {
AvlNode *node2, *node3;
if( avlBalance( from->left ) == -1 ) {
//left-left
node2 = from->left;
from->left = node2->right;
node2->right = from;
avlSetHeight( from );
avlSetHeight( node2 );
return node2;
} else {
//left-right
node2 = from->left;
node3 = node2->right;
from->left = node3->right;
node2->right = node3->left;
node3->left = node2;
node3->right = from;
avlSetHeight( from );
avlSetHeight( node2 );
avlSetHeight( node3 );
return node3;
}
} else if( balance == 2 ) {
AvlNode *node2, *node3;
if( avlBalance( from->right ) == 1 ) {
//right-right
node2 = from->right;
from->right = node2->left;
node2->left = from;
avlSetHeight( from );
avlSetHeight( node2 );
return node2;
} else {
//right-left
node2 = from->right;
node3 = node2->left;
from->right = node3->left;
node2->left = node3->right;
node3->right = node2;
node3->left = from;
avlSetHeight( from );
avlSetHeight( node2 );
avlSetHeight( node3 );
return node3;
}
}
}
//if no balances occured, this node
//remains the root of this subtree
return from;
}
