Question

I have an array of java objects.

• Each object stores two longs that define a number range.
• I already have a guarantee that for all the objects in the range, the number ranges don’t overlap.

I want a quick of finding a particular object in the array, given a number which may (or may not) fall within one of the number ranges defined by the objects.

I was hoping to do this using Array.binarySearch but that doesn’t look appropriate.

Any thoughts on the best way to do this?

Answer 1

Use a TreeMap. The key is the lower of the two Long range bounds; the value is the object.

private TreeMap<Long, T> map = new TreeMap<Long, T>();

void insertObject(T object) {
    map.put(object, object.getLowerRangeBoundary());
}

T getObjectByKeyInRange(Long query) {
    // Get the first Object in the tree that corresponds with the query
    Map.Entry<Long, T> e = map.floorEntry(query);

    // If there's no entry, then the query value is lower than all ranges in the tree
    if (e == null) {
        return null;
    }

    T target = e.getValue();
    // "target" is the only object that can contain the query value
    // If the query value is within the range of "target", then it is our object
    if (query < target.getUpperRangeBoundary()) {
        return target;
    }

    // Nobody has the query value in their range; return null
    return null;
}