Implementation of Finger Tree, an immutable general-purpose data structure which can further be used to implement random-access sequences, priority-queues, ordered sequences, interval trees, etc.
Based on: Ralf Hinze and Ross Paterson, "Finger trees: a simple general-purpose data structure".
Note that Finger Tree is not meant to be used on its own. Instead, it should serve as an infrastructure for building other data structures. As an example, immutable-sequence.js is an immutable random-access sequence implementation built on top of this library.
Download the js file and include it in your web page.
<script type="text/javascript" src="./fingertree.js"></script>If you want to use it in Node.js, you may install it via npm.
npm install fingertree
Then, in your program:
var FingerTree = require('fingertree');// Create a finger-tree from an array
// By default, the tree is annotated with a size measurer.
var tree = FingerTree.fromArray([1, 2, 3, 4]);
tree.measure(); // 4
tree.peekFirst(); // 1
tree.peekLast(); // 4
// Create a new tree with an element added to the front
var tree2 = tree.addFirst(0);
tree2.peekFirst(); // 0
// Create a new tree with an element added to the end
var tree3 = tree.addLast(5);
tree3.peekLast(); // 5
// Create a new tree with the first element removed
var tree4 = tree.removeFirst();
tree4.peekFirst(); // 2
// Create a new tree with the last element removed
var tree5 = tree.removeLast();
tree5.peekLast(); // 3
// Split into two trees with a predicate on measure.
var split = tree.split(function (measure) {
return measure > 3;
});
split[0].measure(); // 3
split[1].measure(); // 1
// Create a finger-tree with a custom measurer.
var measurer = {
identity: function () {
return -Infinity;
},
measure: function (x) {
return x;
},
sum: function (a, b) {
return Math.max(a, b);
}
};
var maxTree = FingerTree.fromArray([1, 3, 2, 9, 7], measurer);
maxTree.measure(); // 9© 2014 Xueqiao Xu <xueqiaoxu@gmail.com>
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