Program to maintain an AVL tree.

#include
#include
#include

#define FALSE 0
#define TRUE 1

struct AVLNode
{
int data ;
int balfact ;
struct AVLNode *left ;
struct AVLNode *right ;
} ;

struct AVLNode * buildtree ( struct AVLNode *, int, int * ) ;
struct AVLNode * deldata ( struct AVLNode *, int, int * ) ;
struct AVLNode * del ( struct AVLNode *, struct AVLNode *, int * ) ;
struct AVLNode * balright ( struct AVLNode *, int * ) ;
struct AVLNode * balleft ( struct AVLNode *, int * ) ;
void display ( struct AVLNode * ) ;
void deltree ( struct AVLNode * ) ;

void main( )
{
struct AVLNode *avl = NULL ;
int h ;

clrscr( ) ;

avl = buildtree ( avl, 20, &h ) ;
avl = buildtree ( avl, 6, &h ) ;
avl = buildtree ( avl, 29, &h ) ;
avl = buildtree ( avl, 5, &h ) ;
avl = buildtree ( avl, 12, &h ) ;
avl = buildtree ( avl, 25, &h ) ;
avl = buildtree ( avl, 32, &h ) ;
avl = buildtree ( avl, 10, &h ) ;
avl = buildtree ( avl, 15, &h ) ;
avl = buildtree ( avl, 27, &h ) ;
avl = buildtree ( avl, 13, &h ) ;

printf ( "\nAVL tree:\n" ) ;
display ( avl ) ;

avl = deldata ( avl, 20, &h ) ;
avl = deldata ( avl, 12, &h ) ;

printf ( "\nAVL tree after deletion of a node:\n" ) ;
display ( avl ) ;

deltree ( avl ) ;

getch( ) ;
}

/* inserts an element into tree */
struct AVLNode * buildtree ( struct AVLNode *root, int data, int *h )
{
struct AVLNode *node1, *node2 ;

if ( !root )
{
root = ( struct AVLNode * ) malloc ( sizeof ( struct AVLNode ) ) ;
root -> data = data ;
root -> left = NULL ;
root -> right = NULL ;
root -> balfact = 0 ;
*h = TRUE ;
return ( root ) ;
}

if ( data < root -> data )
{
root -> left = buildtree ( root -> left, data, h ) ;
/* If left subtree is higher */
if ( *h )
{
switch ( root -> balfact )
{
case 1:
node1 = root -> left ;
if ( node1 -> balfact == 1 )
{
printf ( "\nRight rotation along %d.", root -> data ) ;
root -> left = node1 -> right ;
node1 -> right = root ;
root -> balfact = 0 ;
root = node1 ;
}
else
{
printf ( "\nDouble rotation, left along %d",
node1 -> data ) ;
node2 = node1 -> right ;
node1 -> right = node2 -> left ;
printf ( " then right along %d.\n", root -> data ) ;
node2 -> left = node1 ;
root -> left = node2 -> right ;
node2 -> right = root ;
if ( node2 -> balfact == 1 )
root -> balfact = -1 ;
else
root -> balfact = 0 ;
if ( node2 -> balfact == -1 )
node1 -> balfact = 1 ;
else
node1 -> balfact = 0 ;
root = node2 ;
}
root -> balfact = 0 ;
*h = FALSE ;
break ;

case 0:
root -> balfact = 1 ;
break ;

case -1:
root -> balfact = 0 ;
*h = FALSE ;
}
}
}

if ( data > root -> data )
{
root -> right = buildtree ( root -> right, data, h ) ;
/* If the right subtree is higher */
if ( *h )
{
switch ( root -> balfact )
{
case 1:
root -> balfact = 0 ;
*h = FALSE ;
break ;

case 0:
root -> balfact = -1 ;
break;

case -1:
node1 = root -> right ;
if ( node1 -> balfact == -1 )
{
printf ( "\nLeft rotation along %d.", root -> data ) ;
root -> right = node1 -> left ;
node1 -> left = root ;
root -> balfact = 0 ;
root = node1 ;
}
else
{
printf ( "\nDouble rotation, right along %d",
node1 -> data ) ;
node2 = node1 -> left ;
node1 -> left = node2 -> right ;
node2 -> right = node1 ;
printf ( " then left along %d.\n", root -> data ) ;
root -> right = node2 -> left ;
node2 -> left = root ;

if ( node2 -> balfact == -1 )
root -> balfact = 1 ;
else
root -> balfact = 0 ;
if ( node2 -> balfact == 1 )
node1 -> balfact = -1 ;
else
node1 -> balfact = 0 ;
root = node2 ;
}
root -> balfact = 0 ;
*h = FALSE ;
}
}
}
return ( root ) ;
}

/* deletes an item from the tree */
struct AVLNode * deldata ( struct AVLNode *root, int data, int *h )
{
struct AVLNode *node ;

if ( !root )
{
printf ( "\nNo such data." ) ;
return ( root ) ;
}
else
{
if ( data < root -> data )
{
root -> left = deldata ( root -> left, data, h ) ;
if ( *h )
root = balright ( root, h ) ;
}
else
{
if ( data > root -> data )
{
root -> right = deldata ( root -> right, data, h ) ;
if ( *h )
root = balleft ( root, h ) ;
}
else
{
node = root ;
if ( node -> right == NULL )
{
root = node -> left ;
*h = TRUE ;
free ( node ) ;
}
else
{
if ( node -> left == NULL )
{
root = node -> right ;
*h = TRUE ;
free ( node ) ;
}
else
{
node -> right = del ( node -> right, node, h ) ;
if ( *h )
root = balleft ( root, h ) ;
}
}
}
}
}
return ( root ) ;
}

struct AVLNode * del ( struct AVLNode *succ, struct AVLNode *node, int *h )
{
struct AVLNode *temp = succ ;
if ( succ -> left != NULL )
{
succ -> left = del ( succ -> left, node, h ) ;
if ( *h )
succ = balright ( succ, h ) ;
}
else
{
temp = succ ;
node -> data = succ -> data ;
succ = succ -> right ;
free ( temp ) ;
*h = TRUE ;
}
return ( succ ) ;
}

/* balances the tree, if right sub-tree is higher */
struct AVLNode * balright ( struct AVLNode *root, int *h )
{
struct AVLNode *node1, *node2 ;

switch ( root -> balfact )
{
case 1:
root -> balfact = 0 ;
break;

case 0:
root -> balfact = -1 ;
*h = FALSE ;
break;

case -1:
node1 = root -> right ;
if ( node1 -> balfact <= 0 )
{
printf ( "\nLeft rotation along %d.", root -> data ) ;
root -> right = node1 -> left ;
node1 -> left = root ;
if ( node1 -> balfact == 0 )
{
root -> balfact = -1 ;
node1 -> balfact = 1 ;
*h = FALSE ;
}
else
{
root -> balfact = node1 -> balfact = 0 ;
}
root = node1 ;
}
else
{
printf ( "\nDouble rotation, right along %d", node1 -> data );
node2 = node1 -> left ;
node1 -> left = node2 -> right ;
node2 -> right = node1 ;
printf ( " then left along %d.\n", root -> data );
root -> right = node2 -> left ;
node2 -> left = root ;

if ( node2 -> balfact == -1 )
root -> balfact = 1 ;
else
root -> balfact = 0 ;
if ( node2 -> balfact == 1 )
node1 -> balfact = -1 ;
else
node1 -> balfact = 0 ;
root = node2 ;
node2 -> balfact = 0 ;
}
}
return ( root ) ;
}

/* balances the tree, if left sub-tree is higher */
struct AVLNode * balleft ( struct AVLNode *root, int *h )
{
struct AVLNode *node1, *node2 ;

switch ( root -> balfact )
{
case -1:
root -> balfact = 0 ;
break ;

case 0:
root -> balfact = 1 ;
*h = FALSE ;
break ;

case 1:
node1 = root -> left ;
if ( node1 -> balfact >= 0 )
{
printf ( "\nRight rotation along %d.", root -> data ) ;
root -> left = node1 -> right ;
node1 -> right = root ;
if ( node1 -> balfact == 0 )
{
root -> balfact = 1 ;
node1 -> balfact = -1 ;
*h = FALSE ;
}
else
{
root -> balfact = node1 -> balfact = 0 ;
}
root = node1 ;
}
else
{
printf ( "\nDouble rotation, left along %d", node1 -> data ) ;
node2 = node1 -> right ;
node1 -> right = node2 -> left ;
node2 -> left = node1 ;
printf ( " then right along %d.\n", root -> data ) ;
root -> left = node2 -> right ;
node2 -> right = root ;

if ( node2 -> balfact == 1 )
root -> balfact = -1 ;
else
root -> balfact = 0 ;
if ( node2-> balfact == -1 )
node1 -> balfact = 1 ;
else
node1 -> balfact = 0 ;
root = node2 ;
node2 -> balfact = 0 ;
}
}
return ( root ) ;
}

/* displays the tree in-order */
void display ( struct AVLNode *root )
{
if ( root != NULL )
{
display ( root -> left ) ;
printf ( "%d\t", root -> data ) ;
display ( root -> right ) ;
}
}

/* deletes the tree */
void deltree ( struct AVLNode *root )
{
if ( root != NULL )
{
deltree ( root -> left ) ;
deltree ( root -> right ) ;
}
free ( root ) ;
}