interval-tree

Introduction

This project consists of two classes: IntervalTree and IntervalSetTree.

IntervalTree is an implementation of a red-black interval-tree for half-open integer intervals. Details can be found either explicitly or as exercises in Introduction to Algorithms. It has the basic functionality one would expect from an interval-tree: insertion, deletion, and overlap query.

IntervalSetTree is a modification of IntervalTree which handles Intervals with the same start and end coordinates, but which differ in some other way, for example, a unique name field. Rather than contain a single Interval, a Node in an IntervalSetTree contains a Set of Intervals, all with the same coordinates. The functionality is otherwise the same, except that many methods will return an Iterator<? extends Interval> rather than an Optional<? extends Interval> since multiple values can be returned.

Why write this?

The short story is that I needed a data structure to represent a collection of gene annotations in the manner that the IntervalSetTree does. I don't know of any implementation online that does this. The simpler IntervalTree is included with the hope that others may find it helpful, since it

1. is documented
2. doesn't have public methods that return null
3. doesn't expose the underlying node structure
4. is tested

Why not use another implementation?

There is a lot of debate on the Internet about which sort of implementation is "best": top-down vs bottom-up, 2-3 vs 2-3-4, etc. Whatever the negatives of the CLRS implementation may be, the benefit is that clear, thorough documentation can be found in any university library.

How do I use this?

Using this classes should be straightforward. In the following examples, Impl implements the Interval interface.

Creating an empty tree

Creating trees is done through the class constructors.

Empty tree:

IntervalTree<Impl> tree = new IntervalTree<>();

One-element tree:

IntervalTree<Impl> tree = new IntervalTree<>(new Impl(1, 100));

Adding intervals

tree.insert(new Impl(3, 10));

This method returns a boolean if the value was added (that is, no duplicate found), so feel free to do something like

if (tree.insert(interval)) {
  celebrate(goodTimes);
} else {
  cry();
}

Querying the tree

Querying the tree is simply

tree.contains(interval)

If you're looking for, say, the maximum value

Impl max = tree.maximum()
               .orElseThrow(() -> new SomeTypeOfException("cant find the max!"));

You can also iterate through the tree

for (Impl i : tree) {
  System.out.println(i.toString);
}

tree.iterator()
    .forEachRemaining( x -> System.out.println(x.toString()) );

Iterator<Impl> i = tree.iterator();
while (i.hasNext()) {
  System.out.println((i.next()).toString());
}

Overlap queries are pretty much the same.

tree.overlappers(someInterval)
    .forEachRemaining( x -> System.out.println(x.toString()) );

Removing intervals

Removing intervals is as you might guess.

if (tree.delete(someInterval)) {
  System.out.println("Get outta here!");
}

if (tree.deleteOverlappers(someInterval)) {
  System.out.println("All y'all get outta here!");
}