Function malachite_base::vecs::exhaustive::lex_unique_vecs_length_range

pub fn lex_unique_vecs_length_range<I: Clone + Iterator>(
    a: u64,
    b: u64,
    xs: I,
) -> LexUniqueVecs<I> 
where
    I::Item: Clone,

Generates Vecs, with lengths in a range $[a, b)$, with elements from a single iterator, such that each Vec has no repeated elements.

The Vecs are ordered lexicographically with respect to the order of the element iterator.

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

The iterator should be finite; if it is infinite, only prefixes of the iterator will be generated.

If $a \leq b$, the output is empty.

If $a = 0$ and $b = 1$, the output consists of a single empty Vec.

If the input iterator is infinite and $0 < a < b$, the output length is also infinite.

If the input iterator length is $n$, the output length is $$ \sum_{i=a}^{b - 1} \frac{n!}{k!}. $$

Examples

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

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