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use std::fmt;
use std::iter::FusedIterator;
use std::usize;
use alloc::vec::Vec;
use super::combinations::{Combinations, combinations};
use super::size_hint;
/// An iterator to iterate through the powerset of the elements from an iterator.
///
/// See [`.powerset()`](crate::Itertools::powerset) for more
/// information.
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct Powerset<I: Iterator> {
combs: Combinations<I>,
// Iterator `position` (equal to count of yielded elements).
pos: usize,
}
impl<I> Clone for Powerset<I>
where I: Clone + Iterator,
I::Item: Clone,
{
clone_fields!(combs, pos);
}
impl<I> fmt::Debug for Powerset<I>
where I: Iterator + fmt::Debug,
I::Item: fmt::Debug,
{
debug_fmt_fields!(Powerset, combs, pos);
}
/// Create a new `Powerset` from a clonable iterator.
pub fn powerset<I>(src: I) -> Powerset<I>
where I: Iterator,
I::Item: Clone,
{
Powerset {
combs: combinations(src, 0),
pos: 0,
}
}
impl<I> Iterator for Powerset<I>
where
I: Iterator,
I::Item: Clone,
{
type Item = Vec<I::Item>;
fn next(&mut self) -> Option<Self::Item> {
if let Some(elt) = self.combs.next() {
self.pos = self.pos.saturating_add(1);
Some(elt)
} else if self.combs.k() < self.combs.n()
|| self.combs.k() == 0
{
self.combs.reset(self.combs.k() + 1);
self.combs.next().map(|elt| {
self.pos = self.pos.saturating_add(1);
elt
})
} else {
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
// Total bounds for source iterator.
let src_total = size_hint::add_scalar(self.combs.src().size_hint(), self.combs.n());
// Total bounds for self ( length(powerset(set) == 2 ^ length(set) )
let self_total = size_hint::pow_scalar_base(2, src_total);
if self.pos < usize::MAX {
// Subtract count of elements already yielded from total.
size_hint::sub_scalar(self_total, self.pos)
} else {
// Fallback: self.pos is saturated and no longer reliable.
(0, self_total.1)
}
}
}
impl<I> FusedIterator for Powerset<I>
where
I: Iterator,
I::Item: Clone,
{}