Arrays and Iteration

Find Maximum

Scan the array once, keeping the largest value seen so far. The replay highlights when a candidate replaces the running maximum.

Algorithm

execution replay The checked-in replay follows the language-neutral state table for `array-find-max`.
cross-language comparison This Kotlin DSA version keeps the same data and final output as every other DSA book in this wave.

Basic Implementation

basic.kt
Replay: real traced execution (multi-file project)
fun main() {
	val arr = intArrayOf(3, 1, 4, 1, 5, 9, 2, 6)
	var best = arr[0]
	for (i in 1 until arr.size) {
		if (arr[i] > best) {
			best = arr[i]
		}
	}
	println(best)
}

  1. arr ← [3, 1, 4, 1, 5, 9, 2, 6], best ← 3

    1fun main() {2	val arr = intArrayOf(3, 1, 4, 1, 5, 9, 2, 6)
    values this step[3, 1, 4, 1, 5, 9, 2, 6]arr3best

  2. replaced ← no

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this stepnoreplaced1i1arr[i]3best

  3. best ← 4, replaced ← yes

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this step3 → 4bestyesreplaced2i4arr[i]

  4. replaced ← no

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this stepnoreplaced3i1arr[i]4best

  5. best ← 5, replaced ← yes

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this step4 → 5bestyesreplaced4i5arr[i]

  6. best ← 9, replaced ← yes

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this step5 → 9bestyesreplaced5i9arr[i]

  7. replaced ← no

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this stepnoreplaced6i2arr[i]9best

  8. replaced ← no

    4for (i in 1 until arr.size) {5	if (arr[i] > best) {6		best = arr[i]
    values this stepnoreplaced7i6arr[i]9best

  9. stdout ← 9

    8	}9	println(best)10}
    values this step9stdout9best

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Kotlin stores the input as a primitive IntArray from intArrayOf(3, 1, 4, 1, 5, 9, 2, 6), so indexed reads return non-null Int values.
  • arr is a val, so the array reference is not rebound. best is a var seeded from arr[0] and is the only scalar state updated during the scan.
  • The loop uses for (i in 1 until arr.size), visiting indexes 1 through 7 and avoiding a second read of the seed element at index 0.
  • if (arr[i] > best) performs a strict Int comparison; equal values do not replace the current maximum.
  • The trace shows replacements at i=2 (3 -> 4), i=4 (4 -> 5), and i=5 (5 -> 9); indexes 1, 3, 6, and 7 leave best unchanged.
  • println(best) uses Kotlin's standard output formatting for the final Int, producing 9.