Function malachite_base::vecs::exhaustive::exhaustive_unique_vecs_fixed_length

pub fn exhaustive_unique_vecs_fixed_length<I: Iterator>(
    k: u64,
    xs: I,
) -> ExhaustiveUniqueVecsFixedLength<I> 
where
    I::Item: Clone,

Generates Vecs of a given length with elements from a single iterator, such that each Vec has no repeated elements.

The source iterator should not repeat any elements, but this is not enforced.

If $k$ is 0, the output length is 1.

If $k$ is nonzero and the input iterator is infinite, the output length is also infinite.

If $k$ is nonzero and the input iterator length is $n$, the output length is $$ (n)_ k = \prod_ {i=0}^{k-1}(n - i) = frac{n!}{(n-k)!}. $$

If $k$ is 0, the output consists of one empty Vec.

If xs is empty, the output is also empty, unless $k$ is 0.

Examples

use itertools::Itertools;
use malachite_base::vecs::exhaustive::exhaustive_unique_vecs_fixed_length;

let xss = exhaustive_unique_vecs_fixed_length(4, 1..=6)
    .take(20)
    .collect_vec();
assert_eq!(
    xss.iter().map(Vec::as_slice).collect_vec().as_slice(),
    &[
        &[1, 2, 3, 4],
        &[1, 2, 3, 5],
        &[1, 2, 4, 3],
        &[1, 2, 4, 5],
        &[1, 3, 2, 4],
        &[1, 2, 5, 3],
        &[1, 3, 4, 2],
        &[1, 3, 4, 5],
        &[1, 4, 2, 3],
        &[1, 3, 2, 5],
        &[1, 4, 3, 2],
        &[1, 2, 5, 4],
        &[2, 1, 3, 4],
        &[1, 3, 5, 2],
        &[2, 1, 4, 3],
        &[2, 3, 4, 5],
        &[2, 3, 1, 4],
        &[1, 5, 2, 3],
        &[2, 3, 4, 1],
        &[1, 4, 2, 5]
    ]
);