1 use std::fmt;
2 use std::usize;
3 use alloc::vec::Vec;
4
5 use super::combinations::{Combinations, combinations};
6 use super::size_hint;
7
8 /// An iterator to iterate through the powerset of the elements from an iterator.
9 ///
10 /// See [`.powerset()`](../trait.Itertools.html#method.powerset) for more
11 /// information.
12 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
13 pub struct Powerset<I: Iterator> {
14 combs: Combinations<I>,
15 // Iterator `position` (equal to count of yielded elements).
16 pos: usize,
17 }
18
19 impl<I> Clone for Powerset<I>
20 where I: Clone + Iterator,
21 I::Item: Clone,
22 {
23 clone_fields!(combs, pos);
24 }
25
26 impl<I> fmt::Debug for Powerset<I>
27 where I: Iterator + fmt::Debug,
28 I::Item: fmt::Debug,
29 {
30 debug_fmt_fields!(Powerset, combs, pos);
31 }
32
33 /// Create a new `Powerset` from a clonable iterator.
powerset<I>(src: I) -> Powerset<I> where I: Iterator, I::Item: Clone,34 pub fn powerset<I>(src: I) -> Powerset<I>
35 where I: Iterator,
36 I::Item: Clone,
37 {
38 Powerset {
39 combs: combinations(src, 0),
40 pos: 0,
41 }
42 }
43
44 impl<I> Iterator for Powerset<I>
45 where
46 I: Iterator,
47 I::Item: Clone,
48 {
49 type Item = Vec<I::Item>;
50
next(&mut self) -> Option<Self::Item>51 fn next(&mut self) -> Option<Self::Item> {
52 if let Some(elt) = self.combs.next() {
53 self.pos = self.pos.saturating_add(1);
54 Some(elt)
55 } else if self.combs.k() < self.combs.n()
56 || self.combs.k() == 0
57 {
58 self.combs.reset(self.combs.k() + 1);
59 self.combs.next().map(|elt| {
60 self.pos = self.pos.saturating_add(1);
61 elt
62 })
63 } else {
64 None
65 }
66 }
67
size_hint(&self) -> (usize, Option<usize>)68 fn size_hint(&self) -> (usize, Option<usize>) {
69 // Total bounds for source iterator.
70 let src_total = size_hint::add_scalar(self.combs.src().size_hint(), self.combs.n());
71
72 // Total bounds for self ( length(powerset(set) == 2 ^ length(set) )
73 let self_total = size_hint::pow_scalar_base(2, src_total);
74
75 if self.pos < usize::MAX {
76 // Subtract count of elements already yielded from total.
77 size_hint::sub_scalar(self_total, self.pos)
78 } else {
79 // Fallback: self.pos is saturated and no longer reliable.
80 (0, self_total.1)
81 }
82 }
83 }
84