Cookies and Greedy Takahashi の解説

これもBTreeSetを使えばやるだけに帰着できます。

fn main() {
    input! {
        n: usize,
        a: [isize; n]
    }
    let mut set = a.into_iter().collect::<BTreeSet<isize>>();
    let mut ans = 0;
    let mut now = 0;
    while !set.is_empty() {
        let &left = set.range(..now).next_back().unwrap_or(&(isize::MIN / 2));
        let &right = set.range(now..).next().unwrap_or(&(isize::MAX / 2));
        let ldiff = now - left;
        let rdiff = right - now;
        if ldiff <= rdiff {
            ans += ldiff;
            now = left;
            set.remove(&left);
        } else {
            ans += rdiff;
            now = right;
            set.remove(&right);
        }
    }
    println!("{}", ans);
}