Binary Search First Occurrence

Find the first copy of a duplicated target by recording matches and continuing to search the left half.

Algorithm

Basic Implementation

basic.kt

fun main() {
	val arr = intArrayOf(1, 2, 4, 4, 4, 7, 9)
	val target = 4
	var lo = 0
	var hi = arr.size - 1
	var result = -1
	while (lo <= hi) {
		val mid = lo + (hi - lo) / 2
		if (arr[mid] == target) {
			result = mid
			hi = mid - 1
		} else if (arr[mid] < target) {
			lo = mid + 1
		} else {
			hi = mid - 1
		}
	}
	println(result)
}

Complexity

Time: O(log n)
Space: O(1)

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-first`.

cross-language comparison This Kotlin DSA version keeps the same data and final output as every other DSA book in this wave.