flat-tree

A series of functions to map a binary tree to a list

npm install flat-tree

Usage

You can represent a binary tree in a simple flat list using the following structure

      3
  1       5
0   2   4   6  ...

This module exposes a series of functions to help you build and maintain this data structure

var tree = require('flat-tree')
var list = []

var i = tree.index(0, 0) // get array index for depth: 0, offset: 0
var j = tree.index(1, 0) // get array index for depth: 1, offset: 0

// use these indexes to store some data

list[i] = 'a'
list[j] = 'b'
list[tree.parent(i)] = 'parent of a and b'

API

index = tree.index(depth, offset)

Returns an array index for the tree element at the given depth and offset

parentIndex = tree.parent(index)

Returns the index of the parent element in tree

siblingIndex = tree.sibling(index)

Returns the index of this elements sibling

children = tree.children(index)

Returns an array [leftChild, rightChild] with the indexes of this elements children. If this element does not have any children it returns null

range = tree.spans(index)

Returns the range (inclusive) the tree root at index spans. For example tree.spans(3) would return [0, 6] (see the usage example).

index = tree.leftSpan(index)

Returns the left spanning in index in the tree index spans.

index = tree.rightSpan(index)

Returns the right spanning in index in the tree index spans.

count = tree.count(index)

Returns how many nodes (including parent nodes) a tree contains

depth = tree.depth(index)

Returns the depth of an element

offset = tree.offset(index, [depth])

Returns the relative offset of an element

roots = tree.fullRoots(index)

Returns a list of all the full roots (subtrees where all nodes have either 2 or 0 children) < index. For example fullRoots(8) returns [3] since the subtree rooted at 3 spans 0 -> 6 and the tree rooted at 7 has a child located at 9 which is >= 8.

iterator = tree.iterator(index)

Create a stateful tree iterator starting at a given index. The iterator exposes the following methods.

index = iterator.next()

Move the iterator the next item in the tree.

index = iterator.prev()

Move the iterator the prev item in the tree.

iterator.seek(index)

Move the iterator the this specific tree index.

index = iterator.parent()

Move the iterator to the current parent index

index = iterator.leftChild()

Move the iterator to the current left child index.

index = iterator.rightChild()

Move the iterator to the current right child index.

index = iterator.leftSpan()

Move the iterator to the current left span index.

index = iterator.rightSpan()

Move the iterator to the current right span index.

bool = iterator.isLeft()

Is the iterator at a left sibling?

bool = iterator.isRight()

Is the iterator at a right sibling?

index = iterator.sibling()

Move the iterator to the current sibling

See also

• mafintosh/print-flat-tree: A cli that can pretty print flat-trees.
• bcomnes/flattree: A port of the node module to Go.
• arablocks/flat-tree.c: A port of the module to C
• datkt/flat-tree: A port of the module to Kotlin
• datrs/flat-tree: A port to Rust.
• bcomnes/flattree: A port to Go.
• noffle/cl-flat-tree: A port to Common Lisp.

License

MIT