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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::integer_polynomial::IntegerPolynomial;
use malachite_base::num::arithmetic::traits::IsUnit;
impl IsUnit for IntegerPolynomial {
/// Determines whether an [`IntegerPolynomial`] is a unit: whether it is the constant polynomial
/// 1 or $-1$, the only polynomials with integer coefficients that have a multiplicative
/// inverse.
///
/// # 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_nz::integer_polynomial::IntegerPolynomial;
///
/// assert_eq!(IntegerPolynomial::one().is_unit(), true);
/// assert_eq!(IntegerPolynomial::negative_one().is_unit(), true);
/// assert_eq!(IntegerPolynomial::ZERO.is_unit(), false);
/// assert_eq!(IntegerPolynomial::two().is_unit(), false);
/// assert_eq!(IntegerPolynomial::x().is_unit(), false);
/// assert_eq!(
/// IntegerPolynomial::from_str("-x-1").unwrap().is_unit(),
/// false
/// );
/// ```
fn is_unit(&self) -> bool {
match self.coefficients.as_slice() {
[c] => c.is_unit(),
_ => false,
}
}
}