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.kt 
fun search(arr: IntArray, 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)
	return search(arr, target, lo, mid - 1)
}

fun main() {
	val arr = intArrayOf(1, 3, 5, 7, 9, 11, 13)
	val target = 11
	println(search(arr, target, 0, arr.size - 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 Kotlin DSA version keeps the same data and final output as every other DSA book in this wave.