itertools/
combinations_with_replacement.rs

1use alloc::vec::Vec;
2use std::fmt;
3use std::iter::FusedIterator;
4
5use super::lazy_buffer::LazyBuffer;
6
7/// An iterator to iterate through all the `n`-length combinations in an iterator, with replacement.
8///
9/// See [`.combinations_with_replacement()`](crate::Itertools::combinations_with_replacement)
10/// for more information.
11#[derive(Clone)]
12pub struct CombinationsWithReplacement<I>
13where
14    I: Iterator,
15    I::Item: Clone,
16{
17    indices: Vec<usize>,
18    pool: LazyBuffer<I>,
19    first: bool,
20}
21
22impl<I> fmt::Debug for CombinationsWithReplacement<I>
23where
24    I: Iterator + fmt::Debug,
25    I::Item: fmt::Debug + Clone,
26{
27    debug_fmt_fields!(Combinations, indices, pool, first);
28}
29
30impl<I> CombinationsWithReplacement<I>
31where
32    I: Iterator,
33    I::Item: Clone,
34{
35    /// Map the current mask over the pool to get an output combination
36    fn current(&self) -> Vec<I::Item> {
37        self.indices.iter().map(|i| self.pool[*i].clone()).collect()
38    }
39}
40
41/// Create a new `CombinationsWithReplacement` from a clonable iterator.
42pub fn combinations_with_replacement<I>(iter: I, k: usize) -> CombinationsWithReplacement<I>
43where
44    I: Iterator,
45    I::Item: Clone,
46{
47    let indices: Vec<usize> = alloc::vec![0; k];
48    let pool: LazyBuffer<I> = LazyBuffer::new(iter);
49
50    CombinationsWithReplacement {
51        indices,
52        pool,
53        first: true,
54    }
55}
56
57impl<I> Iterator for CombinationsWithReplacement<I>
58where
59    I: Iterator,
60    I::Item: Clone,
61{
62    type Item = Vec<I::Item>;
63    fn next(&mut self) -> Option<Self::Item> {
64        // If this is the first iteration, return early
65        if self.first {
66            // In empty edge cases, stop iterating immediately
67            return if !(self.indices.is_empty() || self.pool.get_next()) {
68                None
69            // Otherwise, yield the initial state
70            } else {
71                self.first = false;
72                Some(self.current())
73            };
74        }
75
76        // Check if we need to consume more from the iterator
77        // This will run while we increment our first index digit
78        self.pool.get_next();
79
80        // Work out where we need to update our indices
81        let mut increment: Option<(usize, usize)> = None;
82        for (i, indices_int) in self.indices.iter().enumerate().rev() {
83            if *indices_int < self.pool.len()-1 {
84                increment = Some((i, indices_int + 1));
85                break;
86            }
87        }
88
89        match increment {
90            // If we can update the indices further
91            Some((increment_from, increment_value)) => {
92                // We need to update the rightmost non-max value
93                // and all those to the right
94                for indices_index in increment_from..self.indices.len() {
95                    self.indices[indices_index] = increment_value;
96                }
97                Some(self.current())
98            }
99            // Otherwise, we're done
100            None => None,
101        }
102    }
103}
104
105impl<I> FusedIterator for CombinationsWithReplacement<I>
106where
107    I: Iterator,
108    I::Item: Clone,
109{}
itertools/combinations_with_replacement.rs

itertools/
combinations_with_replacement.rs
