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// Copyright © 2026 Mikhail Hogrefe
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
use crate::rational_polynomial::RationalPolynomial;
use malachite_base::num::arithmetic::traits::IsUnit;
impl IsUnit for RationalPolynomial {
/// Determines whether a [`RationalPolynomial`] is a unit: whether it is a nonzero constant,
/// which is exactly when it has a multiplicative inverse, since the coefficients form a field.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::IsUnit;
/// use malachite_base::num::basic::traits::Zero;
/// use malachite_base::polynomial::Polynomial;
/// use malachite_q::rational_polynomial::RationalPolynomial;
///
/// assert_eq!(RationalPolynomial::one().is_unit(), true);
/// assert_eq!(RationalPolynomial::two().is_unit(), true);
/// assert_eq!(RationalPolynomial::one_half().is_unit(), true);
/// assert_eq!(
/// RationalPolynomial::from_str("-22/7").unwrap().is_unit(),
/// true
/// );
/// assert_eq!(RationalPolynomial::ZERO.is_unit(), false);
/// assert_eq!(RationalPolynomial::x().is_unit(), false);
/// assert_eq!(
/// RationalPolynomial::from_str("1/2*x+1").unwrap().is_unit(),
/// false
/// );
/// ```
#[inline]
fn is_unit(&self) -> bool {
self.numerator.coefficients_asc().len() == 1
}
}