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use alloc::collections::BinaryHeap;
use core::cmp::Ord;
pub(crate) fn k_smallest<T: Ord, I: Iterator<Item = T>>(mut iter: I, k: usize) -> BinaryHeap<T> {
if k == 0 { return BinaryHeap::new(); }
let mut heap = iter.by_ref().take(k).collect::<BinaryHeap<_>>();
iter.for_each(|i| {
debug_assert_eq!(heap.len(), k);
// Equivalent to heap.push(min(i, heap.pop())) but more efficient.
// This should be done with a single `.peek_mut().unwrap()` but
// `PeekMut` sifts-down unconditionally on Rust 1.46.0 and prior.
if *heap.peek().unwrap() > i {
*heap.peek_mut().unwrap() = i;
}
});
heap
}