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 Rust DSA version keeps the same data and final output as every other DSA book in this wave.

Basic Implementation

basic.rs
Replay: real traced execution (multi-file project)
fn main() {
	let arr = [3, 1, 4, 1, 5, 9, 2, 6];
	let mut best = arr[0];
	for i in 1..arr.len() {
		if arr[i] > best {
			best = arr[i];
		}
	}
	println!("{}", best);
}

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

    1fn main() {2	let arr = [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..arr.len() {5	if arr[i] > best {6		best = arr[i];
    values this stepnoreplaced1i1arr[i]3best

  3. best ← 4, replaced ← yes

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

  4. replaced ← no

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

  5. best ← 5, replaced ← yes

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

  6. best ← 9, replaced ← yes

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

  7. replaced ← no

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

  8. replaced ← no

    4for i in 1..arr.len() {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

  • The checked source uses a fixed array literal, let arr = [3, 1, 4, 1, 5, 9, 2, 6], not a Vec.
  • let mut best = arr[0] copies the first i32 value into a mutable local; the array itself is never mutated.
  • The loop is index-based: for i in 1..arr.len(). Each arr[i] read is bounds checked by Rust, and the exclusive range keeps i within the array length.
  • Comparisons use copied integer values. When arr[i] > best, assignment best = arr[i] copies the new scalar into the local.
  • The trace records replacements at i=2 (4), i=4 (5), and i=5 (9); scans at i=1, i=3, i=6, and i=7 leave best unchanged.
  • println!("{}", best) uses the display formatter for the final integer and prints 9.