Day 12: Vectors

Vec<T> is Rust's dynamic array - it can grow and shrink at runtime.

Creating Vectors

let v1: Vec<i32> = Vec::new();       // Empty vector
let v2 = vec![1, 2, 3];              // Using vec! macro
let v3 = Vec::with_capacity(10);     // Pre-allocated

Modifying Vectors

let mut v = vec![1, 2, 3];
v.push(4);           // Add to end
v.pop();             // Remove from end, returns Option<T>
v.insert(0, 10);     // Insert at index
v.remove(0);         // Remove at index

Accessing Elements

let v = vec![1, 2, 3, 4, 5];

// By index (panics if out of bounds)
let third = v[2];

// Safe access with get (returns Option)
match v.get(2) {
    Some(val) => println!("{}", val),
    None => println!("No element"),
}

Iterating

for item in &v {
    println!("{}", item);
}

// With mutable reference
for item in &mut v {
    *item += 1;
}

Vectors are crucial for collecting iterator results with .collect()!

The Task

Implement sum_and_max(numbers) that returns (sum, max) of a slice.

Requirements

Take &[i32] (slice, not Vec)
Return (sum, max) as a tuple
Input: [3, 1, 4, 1, 5, 9, 2, 6]
Output: (31, 9)

Hints

fn sum_and_max(numbers: &[i32]) -> (i32, i32) {
    let sum = numbers.iter().sum();
    let max = *numbers.iter().max().unwrap();
    (sum, max)
}

Or manually:

let mut sum = 0;
let mut max = numbers[0];
for &n in numbers {
    sum += n;
    if n > max { max = n; }
}