Spheniscine - recursive closure example

    struct Dp<'a> {
        f: &'a dyn Fn(&Dp, u64, usize) -> u64
    }

    let memo = RefCell::new(HashMap::new());
    let dp = Dp {
        f: &|dp, x, i| {
            if let Some(res) = memo.borrow().get(&(x, i)) { return *res; }
            let res = if i == n-1 {
                x / A[i]
            } else {
                let fl = x.div_floor(A[i+1]) * A[i+1];
                let ce = x.div_ceil(A[i+1]) * A[i+1];

                min((x - fl) / A[i] + (dp.f)(dp, fl, i+1), (ce - x) / A[i] + (dp.f)(dp, ce, i+1))
            };

            memo.borrow_mut().insert((x, i), res);
            res
        }
    };

    let ans = (dp.f)(&dp, x, 0);