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use std::fmt;
use super::lazy_buffer::LazyBuffer;
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct Combinations<I: Iterator> {
indices: Vec<usize>,
pool: LazyBuffer<I>,
first: bool,
}
impl<I> Clone for Combinations<I>
where I: Clone + Iterator,
I::Item: Clone,
{
clone_fields!(indices, pool, first);
}
impl<I> fmt::Debug for Combinations<I>
where I: Iterator + fmt::Debug,
I::Item: fmt::Debug,
{
debug_fmt_fields!(Combinations, indices, pool, first);
}
pub fn combinations<I>(iter: I, k: usize) -> Combinations<I>
where I: Iterator
{
let mut pool: LazyBuffer<I> = LazyBuffer::new(iter);
for _ in 0..k {
if !pool.get_next() {
break;
}
}
Combinations {
indices: (0..k).collect(),
pool,
first: true,
}
}
impl<I> Iterator for Combinations<I>
where I: Iterator,
I::Item: Clone
{
type Item = Vec<I::Item>;
fn next(&mut self) -> Option<Self::Item> {
if self.first {
if self.pool.is_done() {
return None;
}
self.first = false;
} else if self.indices.len() == 0 {
return None;
} else {
let mut i: usize = self.indices.len() - 1;
if self.indices[i] == self.pool.len() - 1 {
self.pool.get_next();
}
while self.indices[i] == i + self.pool.len() - self.indices.len() {
if i > 0 {
i -= 1;
} else {
return None;
}
}
self.indices[i] += 1;
for j in i+1..self.indices.len() {
self.indices[j] = self.indices[j - 1] + 1;
}
}
Some(self.indices.iter().map(|i| self.pool[*i].clone()).collect())
}
}