AVL(2) AVL(2)
NAME
avlcreate, avlinsert, avldelete, avllookup, avlnext, avlprev
- Balanced binary search tree routines
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <avl.h>
typedef struct Avl Avl;
typedef struct Avltree Avltree;
struct Avl {
Avl *c[2]; /* children */
Avl *p; /* parent */
schar balance; /* balance factor */
};
struct Avltree {
int (*cmp)(Avl*, Avl*);
Avl *root;
};
Avltree *avlcreate(int(*cmp)(Avl*, Avl*));
Avl *avlinsert(Avltree *tree, Avl *new);
Avl *avldelete(Avltree *tree, Avl *key);
Avl *avllookup(Avltree *tree, Avl *key, int dir);
Avl *avlmin(Avltree *tree);
Avl *avlmax(Avltree *tree);
Avl *avlnext(Avl *n);
Avl *avlprev(Avl *n);
DESCRIPTION
These routines allow creation and maintenance of in-memory
balanced binary search trees.
An empty tree is created by calling avlcreate with a compar-
ison function as an argument. The comparison function must
take two pointers to Avl structures and return an integer
less than, equal to, or greater than 0 as the first is
respectively less than, equal to, or greater than the sec-
ond.
Avlinsert adds a new node into the tree and returns an
existing node with the same key that has been removed from
the tree and may be freed. Avllookup searches for a given
key and returns the closest node less than the given key,
equal to, or the closest node greater than the key depending
on whether dir is less than, equal to, or greater than zero,
respectively. If dir is zero and there is no matching key,
Page 1 Plan 9 (printed 12/21/24)
AVL(2) AVL(2)
it returns nil. Avldelete removes the node matching the key
from the tree and returns it. It returns nil if no matching
key is found.
Avlmin returns the minimum Avl node in the tree and avlmax
returns the maximum node. Avlnext returns the next Avl node
in an in-order walk of the AVL tree and avlprev returns the
previous node.
EXAMPLES
Intended usage is to embed the Avl structure anonymously.
For example, the following will create a key-value store
with strings as keys and integers as values.
typedef struct Node {
Avl;
char *key;
int val;
} Node;
int
nodecmp(Avl *la, Avl *lb)
{
Node *a, *b;
a = (Node*)la;
b = (Node*)lb;
return strcmp(a->key, b->key);
}
int
get(Avltree *t, char *key)
{
Node *h, n;
n.key = key;
h = (Node*)avllookup(t, &n);
return h ? h->val : -1;
}
...
Avltree *t = avlcreate(nodecmp);
SOURCE
/sys/src/libavl
SEE ALSO
Donald Knuth, ``The Art of Computer Programming'', Volume 3. Section 6.2.3
DIAGNOSTICS
Avlcreate returns nil on error.
Page 2 Plan 9 (printed 12/21/24)
AVL(2) AVL(2)
HISTORY
This implementation was written for 9front (Dec, 2016).
Page 3 Plan 9 (printed 12/21/24)