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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::num::arithmetic::traits::ContentChained;
use crate::num::basic::unsigneds::PrimitiveUnsigned;
use crate::unsigned_vector::UnsignedVector;
// Returns the GCD of `gcd` and the elements of `xs`. Zeros at either end are skipped, an element of
// 1 at either end gives 1 at once, and the rest are taken in pairs from both ends, stopping as soon
// as the GCD reaches 1.
//
// This is equivalent to `_fmpz_vec_content_chained` from `fmpz_vec/content_chained.c`, FLINT 3.6.0.
pub(crate) fn content_chained<T: PrimitiveUnsigned>(xs: &[T], mut gcd: T) -> T {
let Some(start) = xs.iter().position(|&c| c != T::ZERO) else {
return gcd;
};
let end = xs.iter().rposition(|&c| c != T::ZERO).unwrap();
let mut xs = &xs[start..=end];
if let [first, .., last] = xs
&& (*first == T::ONE || *last == T::ONE)
{
return T::ONE;
}
while gcd != T::ONE
&& let [first, middle @ .., last] = xs
{
gcd.gcd_assign(first.gcd(*last));
xs = middle;
}
if gcd != T::ONE
&& let [middle] = xs
{
gcd.gcd_assign(*middle);
}
gcd
}
impl<T: PrimitiveUnsigned> ContentChained<T> for UnsignedVector<T> {
type Output = T;
/// Computes the GCD of `x` and the elements of an [`UnsignedVector`], taking the vector by
/// value.
///
/// The GCD of `x` and the elements of the 0-dimensional vector, or of a vector of zeros, is
/// `x`. The computation stops as soon as the GCD reaches 1.
///
/// $$
/// f(v, x) = \gcd(x, v_0, v_1, \ldots, v_{n-1}),
/// $$
///
/// where $n$ is the dimension of $v$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ContentChained;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(6, 4, 10)").unwrap();
/// assert_eq!(v.clone().content_chained(4), 2);
/// assert_eq!(v.content_chained(0), 2);
/// let v = UnsignedVector::<u8>::from_str("()").unwrap();
/// assert_eq!(v.content_chained(6), 6);
/// ```
///
/// This is equivalent to `_fmpz_vec_content_chained` from `fmpz_vec/content_chained.c`, FLINT
/// 3.6.0.
#[inline]
fn content_chained(self, x: T) -> T {
content_chained(&self.elements, x)
}
}
impl<T: PrimitiveUnsigned> ContentChained<T> for &UnsignedVector<T> {
type Output = T;
/// Computes the GCD of `x` and the elements of an [`UnsignedVector`], taking the vector by
/// reference.
///
/// The GCD of `x` and the elements of the 0-dimensional vector, or of a vector of zeros, is
/// `x`. The computation stops as soon as the GCD reaches 1.
///
/// $$
/// f(v, x) = \gcd(x, v_0, v_1, \ldots, v_{n-1}),
/// $$
///
/// where $n$ is the dimension of $v$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.dimension()`.
///
/// # Examples
/// ```
/// use core::str::FromStr;
/// use malachite_base::num::arithmetic::traits::ContentChained;
/// use malachite_base::unsigned_vector::UnsignedVector;
///
/// let v = UnsignedVector::<u8>::from_str("(6, 4, 10)").unwrap();
/// assert_eq!((&v).content_chained(4), 2);
/// assert_eq!((&v).content_chained(0), 2);
/// let v = UnsignedVector::<u8>::from_str("()").unwrap();
/// assert_eq!((&v).content_chained(6), 6);
/// ```
///
/// This is equivalent to `_fmpz_vec_content_chained` from `fmpz_vec/content_chained.c`, FLINT
/// 3.6.0.
#[inline]
fn content_chained(self, x: T) -> T {
content_chained(&self.elements, x)
}
}