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Applied Intermediate

12 Iterators

Iterator chains replace most hand-written loops. Build a value by chaining adaptors and finishing with a consumer like sum or collect.

Step 3 / 3

In argmax, return the index of the largest element -- enumerate plus max_by_key, no loop.

Hints

.enumerate() turns items into (index, item) pairs.
max_by_key picks the pair by its value; a final .map(|(i, _)| i) keeps just the index.

12_iterators.rs

// index of the largest element, or None if empty
fn argmax(v: &[i32]) -> Option<usize> {
    todo!()
}

// index of the largest element, or None if empty
fn argmax(v: &[i32]) -> Option<usize> {
    todo!()
}

Reset to starterCompiled in a sandbox; hidden checks must pass.

Reveal solution

fn argmax(v: &[i32]) -> Option<usize> {
    v.iter().enumerate().max_by_key(|&(_, val)| val).map(|(i, _)| i)
}