Searching

Binary Search (Recursive)

Use the same binary-search window as the iterative lesson, but pass lo and hi through recursive calls.

Algorithm

Basic Implementation

basic.scala 
object Main {
	def search(arr: Array[Int], target: Int, lo: Int, hi: Int): Int = {
		if (lo > hi) return -1
		val mid = lo + (hi - lo) / 2
		if (arr(mid) == target) return mid
		if (arr(mid) < target) return search(arr, target, mid + 1, hi)
		search(arr, target, lo, mid - 1)
	}

	def main(args: Array[String]): Unit = {
		val arr = Array(1, 3, 5, 7, 9, 11, 13)
		val target = 11
		println(search(arr, target, 0, arr.length - 1))
	}
}

Complexity

  • Time: O(log n)
  • Space: O(log n) call stack

Implementation notes

  • Keep the explicit control flow. Library shortcuts would hide the state changes this lesson is meant to replay.
  • The final output is intentionally small and deterministic for cross-language comparison.
execution replay The checked-in replay follows the language-neutral state table for `search-binary-recursive`.
cross-language comparison This Scala DSA version keeps the same data and final output as every other DSA book in this wave.