#![allow(unused_variables)]
fn main() {
    use std::collections::VecDeque;
    let mut deque = VecDeque::new();
    deque.push_back(0);
    deque.push_back(1);
    deque.push_front(10);
    deque.push_front(9);
    let mut update_nth = |index: usize, val: u32| {
        let (front, back) = deque.as_mut_slices();
        if index > front.len() - 1 {
            back[index - front.len()] = val;
        } else {
            front[index] = val;
        }
    };
    update_nth(0, 42);
    update_nth(2, 24);
    let v: Vec<_> = deque.into();
    assert_eq!(v, [42, 10, 24, 1]);
}