permutation-generator 0.1.3

A direct permutation generator
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134

use crate::{PResult, PermutationGeneratorError, SinglePermutation8, factorial::factorial16};

#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct PermutationGenerator8Gen {
    nb_elems: u8,
    nb_perms: u16,
    next_idx: u16,
}

impl PermutationGenerator8Gen {
    const MAX_ELEMENTS: u8 = 8;

    pub fn new(nb_elems: u8) -> PResult<Self> {
        Self::check_nb_elems(nb_elems)?;
        Ok(Self {
            next_idx: 0,
            nb_perms: factorial16(nb_elems),
            nb_elems,
        })
    }

    pub fn next_permutation(&mut self) -> Option<impl Iterator<Item = u8>> { self.nth(0) }

    pub fn nth_absolute(nb_elems: u8, idx: u16) -> PResult<Option<impl Iterator<Item = u8>>> {
        Self::check_nb_elems(nb_elems)?;
        Ok(SinglePermutation8::new_precalculated(nb_elems, factorial16(nb_elems), idx))
    }

    pub fn nth(&mut self, step: u16) -> Option<impl Iterator<Item = u8>> {
        let step_result = self.next_idx.saturating_add(step);
        let res = SinglePermutation8::new_precalculated(self.nb_elems, self.nb_perms, step_result);
        self.next_idx = step_result + 1;
        res
    }

    #[must_use]
    pub fn nb_remaining(&self) -> usize { (self.nb_perms - self.next_idx) as usize }

    #[inline]
    fn check_nb_elems(nb_elems: u8) -> PResult<()> {
        if nb_elems > Self::MAX_ELEMENTS {
            Err(PermutationGeneratorError::TooManyElements)
        } else {
            Ok(())
        }
    }
}

impl Iterator for PermutationGenerator8Gen {
    type Item = impl Iterator<Item = u8>;

    fn next(&mut self) -> Option<Self::Item> { self.next_permutation() }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let nb_remaining = self.nb_remaining();
        (nb_remaining, Some(nb_remaining))
    }

    fn count(self) -> usize { self.nb_remaining() }
}

#[cfg(test)]
mod tests {
    use std::iter::Iterator;

    use super::{PermutationGenerator8Gen, PermutationGeneratorError};
    use crate::factorial::factorial16;

    const NB_ELEMS: u8 = 4;

    fn test_slice(ref_slice: &[u8], some_iter: Option<impl Iterator<Item = u8>>) {
        assert_eq!(ref_slice, some_iter.unwrap().collect::<Vec<_>>().as_slice());
    }

    #[test]
    fn new() {
        let pg = PermutationGenerator8Gen::new(14);
        assert_eq!(PermutationGeneratorError::TooManyElements, pg.unwrap_err());
    }

    #[test]
    fn zero() {
        let mut pg = PermutationGenerator8Gen::new(0).unwrap();
        assert!(pg.next_permutation().is_none());
    }

    #[test]
    fn next_permutation() {
        let mut pg = PermutationGenerator8Gen::new(NB_ELEMS).unwrap();
        test_slice(&[0, 1, 2, 3], pg.next_permutation());
        test_slice(&[0, 1, 3, 2], pg.next_permutation());

        let mut pg = PermutationGenerator8Gen::new(NB_ELEMS + 1).unwrap();
        test_slice(&[0, 1, 2, 3, 4], pg.next_permutation());
        test_slice(&[0, 1, 2, 4, 3], pg.next_permutation());
    }

    #[test]
    fn nth_absolute() {
        test_slice(&[0, 1, 2, 3], PermutationGenerator8Gen::nth_absolute(NB_ELEMS, 0).unwrap());
        test_slice(
            &[3, 2, 1, 0],
            PermutationGenerator8Gen::nth_absolute(NB_ELEMS, factorial16(NB_ELEMS) - 1).unwrap(),
        );
        test_slice(
            &[4, 3, 2, 1, 0],
            PermutationGenerator8Gen::nth_absolute(NB_ELEMS + 1, factorial16(NB_ELEMS + 1) - 1)
                .unwrap(),
        );
    }

    #[test]
    fn nth() {
        let mut pg = PermutationGenerator8Gen::new(NB_ELEMS).unwrap();
        test_slice(&[3, 2, 1, 0], pg.nth(factorial16(NB_ELEMS) - 1));
        assert!(pg.next_permutation().is_none());

        let mut pg = PermutationGenerator8Gen::new(NB_ELEMS).unwrap();
        test_slice(&[0, 1, 2, 3], pg.nth(0));
        test_slice(&[3, 2, 1, 0], pg.nth(factorial16(NB_ELEMS) - 2));
    }

    #[test]
    #[allow(clippy::cast_possible_truncation)]
    fn iter() {
        let list = PermutationGenerator8Gen::new(NB_ELEMS)
            .unwrap()
            .map(Iterator::collect::<Vec<_>>)
            .collect::<Vec<_>>();
        assert_eq!(factorial16(NB_ELEMS) as usize, list.len());
        assert_eq!(&[0, 1, 2, 3], list[0].as_slice());
        assert_eq!(&[3, 2, 1, 0], list[factorial16(NB_ELEMS) as usize - 1].as_slice());
    }
}