Arrays and Iteration

Linear Search

Walk an array once looking for a target value. Return the index of the first match, or -1 if none. The simplest possible search loop.

Algorithm

Canonical input arr = [4, 7, 1, 9, 3, 8] with target = 9 finishes after four compares; the matching index is 3.

Basic Implementation

basic.scala 
object Main {
	def linearSearch(arr: Array[Int], target: Int): Int = {
		for (i <- arr.indices) {
			if (arr(i) == target) {
				return i
			}
		}
		-1
	}

	def main(args: Array[String]): Unit = {
		val arr = Array(4, 7, 1, 9, 3, 8)
		val target = 9
		val result = linearSearch(arr, target)
		println(result)
	}
}

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Scala: explicit for (i <- arr.indices) with an early return i the moment arr(i) == target. The stdlib arr.indexOf(target) would hide the walk the lesson is teaching.
  • Method signature def linearSearch(arr: Array[Int], target: Int): Int documents the array contract; the -1 sentinel mirrors the language-neutral spec rather than returning Option[Int].
  • The replay shows the running index, the element being checked, and a match indicator on each frame.
early exit Return the index the moment `arr(i)` equals the target. Walking past it would defeat the point.
sentinel return A no-match walk falls off the loop and returns `-1`.