permutation_generator/single_permutation/
single_permutation_16.rs

1use bit_index::BitIndex16;
2
3#[derive(Debug, Clone, PartialEq, Eq, Hash)]
4pub struct SinglePermutation16 {
5    elems:       BitIndex16,
6    next_mod:    u64,
7    current_idx: u64,
8}
9
10impl SinglePermutation16 {
11    #[must_use]
12    pub fn new(nb_elems: u8, nb_perms: u64, idx: u64) -> Option<Self> {
13        if idx >= nb_perms {
14            None
15        } else {
16            Some(Self {
17                elems:       BitIndex16::new(nb_elems).unwrap(),
18                next_mod:    nb_perms / u64::from(nb_elems),
19                current_idx: idx,
20            })
21        }
22    }
23
24    #[inline]
25    #[must_use]
26    pub fn nb_remaining(&self) -> usize { self.elems.nb_elements() as usize }
27}
28
29impl Iterator for SinglePermutation16 {
30    type Item = u8;
31
32    #[allow(clippy::cast_possible_truncation)]
33    fn next(&mut self) -> Option<Self::Item> {
34        if self.elems.nb_elements() == 0 {
35            return None;
36        }
37        let bit_nb = self.current_idx / self.next_mod;
38        self.current_idx -= bit_nb * self.next_mod;
39        self.next_mod /= u64::from(self.elems.nb_elements()).saturating_sub(2) + 1;
40        self.elems.pop(bit_nb as u8)
41    }
42
43    fn size_hint(&self) -> (usize, Option<usize>) {
44        let nb_remaining = self.nb_remaining();
45        (nb_remaining, Some(nb_remaining))
46    }
47
48    fn count(self) -> usize { self.nb_remaining() }
49}
50
51#[cfg(test)]
52mod tests {
53    use crate::{SinglePermutation16, factorial::factorial64};
54
55    fn single_perm(nb_elems: u8, idx: u64) -> Option<SinglePermutation16> {
56        SinglePermutation16::new(nb_elems, factorial64(nb_elems), idx)
57    }
58
59    #[test]
60    fn new() {
61        assert_eq!(None, single_perm(10, 3_628_800));
62    }
63
64    #[test]
65    fn new_unchecked_iterator() {
66        assert_eq!(
67            &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
68            single_perm(10, 0).unwrap().collect::<Vec<_>>().as_slice()
69        );
70
71        assert_eq!(
72            &[1, 0, 2, 3, 4, 5, 6, 7, 8, 9],
73            single_perm(10, 362_880).unwrap().collect::<Vec<_>>().as_slice()
74        );
75
76        assert_eq!(
77            &[2, 0, 1, 3, 4, 5, 6, 7, 8, 9],
78            single_perm(10, 362_880 * 2).unwrap().collect::<Vec<_>>().as_slice()
79        );
80
81        assert_eq!(
82            &[3, 0, 1, 2, 4, 5, 6, 7, 8, 9],
83            single_perm(10, 362_880 * 3).unwrap().collect::<Vec<_>>().as_slice()
84        );
85
86        assert_eq!(
87            &[9, 8, 7, 6, 5, 4, 3, 2, 1, 0],
88            single_perm(10, 3_628_800 - 1).unwrap().collect::<Vec<_>>().as_slice()
89        );
90    }
91}
permutation_generator/single_permutation/single_permutation_16.rs

permutation_generator/single_permutation/
single_permutation_16.rs
