avl-promise/README.md

Largely copied from avl (https://www.npmjs.com/package/avl), but with a Promise-based comparator!

# AVL tree 

Promise-based [AVL-tree](https://en.wikipedia.org/wiki/AVL_tree):
Largely copied from [avl](https://www.npmjs.com/package/avl), but the
comparator function returns a Promise!

Existing AVL modules perform all operations synchronously. But what if
your custom `comparator` function is asynchronous? -- for example, if
you need to perform a database query, a network request or wait
for a user's input.

[avl-promise](https://www.npmjs.com/package/avl-promise) to the
rescue! However, the performance takes a hit -- even if your async
comparator immediatly resolves to a numeric value. So, **use with
caution and at your own risk**.

| Operation     | Average       | Worst case   |
| ------------- | ------------- | ------------ |
| Space         | **O(n)**      | **O(n)**     |
| Search        | **O(log n)**  | **O(log n)** |
| Insert        | **O(log n)**  | **O(log n)** |
| Delete        | **O(log n)**  | **O(log n)** |

## Install

```shell
npm i -S avl-promise
```

```js
import AVLTree from 'avl-promise';
const tree = new AVLTree();
```

Or use the compiled version 'dist/avl-promise.js'.

[Try it in your browser](https://npm.runkit.com/avl-promise)

## API

### Synchronous methods

* `new AVLTree([compare], [noDuplicates:Boolean])`, where `compare` is optional comparison Promise-returning function
* `tree.at(index:Number):Node|Null` - Return node by its index in sorted order of keys
* `tree.forEach(function(node) {...}):Tree` In-order traversal
* `tree.keys():Array<key>` - Returns the array of keys in order
* `tree.values():Array<*>` - Returns the array of data fields in order
* `tree.pop():Node` - Removes smallest node
* `tree.min():key` - Returns min key
* `tree.max():key` - Returns max key
* `tree.minNode():Node` - Returns the node with smallest key
* `tree.maxNode():Node` - Returns the node with highest key
* `tree.prev(node):Node` - Predecessor node
* `tree.next(node):Node` - Successor node

### Promise methods

The following methods are dependent on the `compare` function and, as
such, return Promises.

* `tree.insert(key:any, [data:any])` - Insert item
* `tree.find(key):Node|Null` - Return node by its key
* `tree.contains(key):Boolean` - Whether a node with the given key is in the tree
* `tree.load(keys:Array<*>, [values:Array<*>]):Tree` - Bulk-load items
* `tree.remove(key:any)` - Remove item
* `tree.range(lo, high, function(node) {} [, context]):Tree` - Walks the range of keys in order. Stops, if the visitor function returns a non-zero value.

**Comparator**

`function(a:key,b:key):Promise(Number)` - Comparator function between two keys, it resolves to:
 * `0` if the keys are equal
 * `<0` if `a < b`
 * `>0` if `a > b`

 The comparator function is extremely important, in case of errors you might end
 up with a wrongly constructed tree or would not be able to retrieve your items.
 It is crucial to test the return values of your `comparator(a,b)` and `comparator(b,a)`
 to make sure it's working correctly, otherwise you may have bugs that are very
 unpredictable and hard to catch.

 **Duplicate keys**

 By default, tree allows duplicate keys. You can disable that by passing `true`
 as a second parameter to the tree constructor. In that case if you would try to
 instert an item with the key, that is already present in the tree, it will not
 be inserted.
 However, the default behavior allows for duplicate keys, cause there are cases
 where you cannot predict that the keys would be unique (example: overlapping
 points in 2D).

## Example

```js
import Tree from 'avl';

const t = new Tree();
t.insert(5)
  .then(t.insert(-10))
  .then(t.insert(0))
  .then(t.insert(33))
  .then(t.insert(2))
  .then(() => {
    console.log(t.keys()); // [-10, 0, 2, 5, 33]
    console.log(t.size);   // 5
    console.log(t.min());  // -10
    console.log(t.max());  // -33

    return t.remove(0);
  })
  .then(() => console.log(t.size));   // 4
```

**Custom comparator (reverse sort)**

```js
import Tree from 'avl';

const t = new Tree((a, b) => b - a);
t.insert(5)
  .then(() => t.insert(-10))
  .then(() => t.insert(0))
  .then(() => t.insert(33))
  .then(() => t.insert(2))
  .then(() => console.log(t.keys())); // [33, 5, 2, 0, -10]
```

**Bulk insert**

```js
import Tree from 'avl';

const t = new Tree();
t.load([3,2,-10,20], ['C', 'B', 'A', 'D'])
  .then(() => {
    console.log(t.keys());   // [-10, 2, 3, 20]
    console.log(t.values()); // ['A', 'B', 'C', 'D']
  });
```

## Benchmarks

```shell
npm run benchmark
```

```
Insert (x1000)
Bintrees x 3,276 ops/sec ±5.03% (71 runs sampled)
Functional red black tree x 1,648 ops/sec ±9.58% (70 runs sampled)
Google Closure library AVL x 564 ops/sec ±8.28% (76 runs sampled)
AVL (sync version) x 5,585 ops/sec ±2.74% (83 runs sampled)
AVL Promise (current) x 2.98 ops/sec ±11.09% (19 runs sampled)
- Fastest is AVL (sync version)

Random read (x1000)
Bintrees x 17,922 ops/sec ±4.22% (82 runs sampled)
Functional red black tree x 12,898 ops/sec ±6.93% (81 runs sampled)
Google Closure library AVL x 21.69 ops/sec ±11.76% (41 runs sampled)
AVL (sync version) x 9,884 ops/sec ±14.96% (65 runs sampled)
AVL Promise (current) x 33.90 ops/sec ±24.63% (48 runs sampled)
- Fastest is Bintrees

Remove (x1000)
Bintrees x 169,381 ops/sec ±5.63% (73 runs sampled)
Functional red black tree x 20,195 ops/sec ±28.25% (62 runs sampled)
Google Closure library AVL x 25,000 ops/sec ±11.19% (77 runs sampled)
AVL (sync version) x 108,944 ops/sec ±1.17% (86 runs sampled)
AVL Promise (current) x 122 ops/sec ±3.17% (70 runs sampled)
- Fastest is Bintrees
```

Adding google closure library to the benchmark is, of course, unfair, cause the
node.js version of it is not optimised by the compiler, but in this case it
plays the role of straight-forward robust implementation.

## Develop

```shell
npm i
npm t
npm run build
```
## Acknowledgements

Many thanks to [Alexander
Milevski](https://github.com/w8r), whoose module
[avl](https://www.npmjs.com/package/avl) was adapted (both the code
and the docs), with just the minimum changes needed to make it work
asynchronously, to create
[avl-promise](https://www.npmjs.com/package/avl-promise).


## License

The MIT License (MIT)

Copyright (c) 2018 André Santos <andrefs@andrefs.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.