Merge pull request #51 from emirpasic/development

Development

LICENSE

@@ -20,4 +20,22 @@ DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+-------------------------------------------------------------------------------
+
+AVL Tree:
+
+Copyright (c) 2017 Benjamin Scher Purcell <benjapurcell@gmail.com>
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

README.md

@@ -24,6 +24,7 @@ Implementation of various data structures and algorithms in Go.
     - [TreeBidiMap](#treebidimap)
   - [Trees](#trees)
     - [RedBlackTree](#redblacktree)
+    - [AVLTree](#avltree)
     - [BTree](#btree)
     - [BinaryHeap](#binaryheap)
 - [Functions](#functions)
@@ -70,6 +71,7 @@ Containers are either ordered or unordered. All ordered containers provide [stat
 | [HashBidiMap](#hashbidimap) | no | no | no | key* |
 | [TreeBidiMap](#treebidimap) | yes | yes* | yes | key* |
 | [RedBlackTree](#redblacktree) | yes | yes* | no | key |
+| [AVLTree](#avltree) | yes | yes* | no | key |
 | [BTree](#btree) | yes | yes* | no | key |
 | [BinaryHeap](#binaryheap) | yes | yes* | no | index |
 |  |  | <sub><sup>*reversible</sup></sub> |  | <sub><sup>*bidirectional</sup></sub> |
@@ -589,6 +591,65 @@ func main() {
 
 Extending the red-black tree's functionality  has been demonstrated in the following [example](https://github.com/emirpasic/gods/blob/master/examples/redblacktreeextended.go).
 
+#### AVLTree
+
+AVL [tree](#trees) is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Lookup, insertion, and deletion all take O(log n) time in both the average and worst cases, where n is the number of nodes in the tree prior to the operation. Insertions and deletions may require the tree to be rebalanced by one or more tree rotations.
+
+AVL trees are often compared with red–black trees because both support the same set of operations and take O(log n) time for the basic operations. For lookup-intensive applications, AVL trees are faster than red–black trees because they are more strictly balanced. <sub><sup>[Wikipedia](https://en.wikipedia.org/wiki/AVL_tree)</sup></sub>
+
+Implements [Tree](#trees) and [ReverseIteratorWithKey](#reverseiteratorwithkey) interfaces.
+
+<p align="center"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/AVL-tree-wBalance_K.svg/262px-AVL-tree-wBalance_K.svg.png" width="300px" height="180px" /><br/><sub>AVL tree with balance factors (green)</sub></p>
+
+```go
+package main
+
+import (
+	"fmt"
+	avl "github.com/emirpasic/gods/trees/avltree"
+)
+
+func main() {
+	tree := avl.NewWithIntComparator() // empty(keys are of type int)
+
+	tree.Put(1, "x") // 1->x
+	tree.Put(2, "b") // 1->x, 2->b (in order)
+	tree.Put(1, "a") // 1->a, 2->b (in order, replacement)
+	tree.Put(3, "c") // 1->a, 2->b, 3->c (in order)
+	tree.Put(4, "d") // 1->a, 2->b, 3->c, 4->d (in order)
+	tree.Put(5, "e") // 1->a, 2->b, 3->c, 4->d, 5->e (in order)
+	tree.Put(6, "f") // 1->a, 2->b, 3->c, 4->d, 5->e, 6->f (in order)
+
+	fmt.Println(tree)
+	//
+	//  AVLTree
+	//  │       ┌── 6
+	//  │   ┌── 5
+	//  └── 4
+	//      │   ┌── 3
+	//      └── 2
+	//          └── 1
+
+
+	_ = tree.Values() // []interface {}{"a", "b", "c", "d", "e", "f"} (in order)
+	_ = tree.Keys()   // []interface {}{1, 2, 3, 4, 5, 6} (in order)
+
+	tree.Remove(2) // 1->a, 3->c, 4->d, 5->e, 6->f (in order)
+	fmt.Println(tree)
+	//
+	//  AVLTree
+	//  │       ┌── 6
+	//  │   ┌── 5
+	//  └── 4
+	//      └── 3
+	//          └── 1
+
+	tree.Clear() // empty
+	tree.Empty() // true
+	tree.Size()  // 0
+}
+```
+
 #### BTree
 
 B-tree is a self-balancing tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree is a generalization of a binary search tree in that a node can have more than two children.
@@ -1255,7 +1316,7 @@ This takes a while, so test within sub-packages:
 
 Biggest contribution towards this library is to use it and give us feedback for further improvements and additions.
 
-For direct contributions, _pull request_ into development branch or ask to become a contributor.
+For direct contributions, _pull request_ into master branch or ask to become a contributor.
 
 Coding style:
 

examples/avltree.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2015, Emir Pasic. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package examples
+
+import (
+	"fmt"
+	avl "github.com/emirpasic/gods/trees/avltree"
+)
+
+// AVLTreeExample to demonstrate basic usage of AVLTree
+func AVLTreeExample() {
+	tree := avl.NewWithIntComparator() // empty(keys are of type int)
+
+	tree.Put(1, "x") // 1->x
+	tree.Put(2, "b") // 1->x, 2->b (in order)
+	tree.Put(1, "a") // 1->a, 2->b (in order, replacement)
+	tree.Put(3, "c") // 1->a, 2->b, 3->c (in order)
+	tree.Put(4, "d") // 1->a, 2->b, 3->c, 4->d (in order)
+	tree.Put(5, "e") // 1->a, 2->b, 3->c, 4->d, 5->e (in order)
+	tree.Put(6, "f") // 1->a, 2->b, 3->c, 4->d, 5->e, 6->f (in order)
+
+	fmt.Println(tree)
+	//
+	//  AVLTree
+	//  │       ┌── 6
+	//  │   ┌── 5
+	//  └── 4
+	//      │   ┌── 3
+	//      └── 2
+	//          └── 1
+
+	_ = tree.Values() // []interface {}{"a", "b", "c", "d", "e", "f"} (in order)
+	_ = tree.Keys()   // []interface {}{1, 2, 3, 4, 5, 6} (in order)
+
+	tree.Remove(2) // 1->a, 3->c, 4->d, 5->e, 6->f (in order)
+	fmt.Println(tree)
+	//
+	//  AVLTree
+	//  │       ┌── 6
+	//  │   ┌── 5
+	//  └── 4
+	//      └── 3
+	//          └── 1
+
+	tree.Clear() // empty
+	tree.Empty() // true
+	tree.Size()  // 0
+}