1 files changed, 20 insertions, 0 deletions
diff --git a/src/k_smallest.rs b/src/k_smallest.rs
new file mode 100644
index 0000000..d58ec70
--- /dev/null
+++ b/src/k_smallest.rs
@@ -0,0 +1,20 @@
+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<_>>();
+
+    for i in iter {
+        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
+}