mdoc.internal.pos.BinarySearch.scala Maven / Gradle / Ivy
package mdoc.internal.pos
import scala.annotation.tailrec
object BinarySearch {
sealed trait ComparisonResult
case object Greater extends ComparisonResult
case object Equal extends ComparisonResult
case object Smaller extends ComparisonResult
/**
* Binary search using a custom compare function.
*
* scala.util.Searching does not support the ability to search an IndexedSeq
* by a custom mapping function, you must search by an element of the same
* type as the elements of the Seq.
*
* @param array Must be sorted according to compare function so that for all
* i > j, compare(array(i), array(i)) == Greater.
* @param compare Callback used at every guess index to determine whether
* the search element has been found, or whether to search
* above or below the guess index.
* @return The first element where compare(element) == Equal. There is no guarantee
* which element is chosen if many elements return Equal.
*/
def array[T](
array: Array[T],
compare: T => ComparisonResult
): Option[T] = {
@tailrec def loop(lo: Int, hi: Int): Option[T] =
if (lo > hi) None
else {
val mid = lo + (hi - lo) / 2
val curr = array(mid)
compare(curr) match {
case Greater => loop(lo, mid - 1)
case Equal => Some(curr)
case Smaller => loop(mid + 1, hi)
}
}
loop(0, array.length - 1)
}
}