1 files changed, 138 insertions, 0 deletions
diff --git a/vendor/itertools/src/k_smallest.rs b/vendor/itertools/src/k_smallest.rs
new file mode 100644
index 00000000..7e4ace26
--- /dev/null
+++ b/vendor/itertools/src/k_smallest.rs
@@ -0,0 +1,138 @@
+use alloc::vec::Vec;
+use core::cmp::Ordering;
+
+/// Consumes a given iterator, returning the minimum elements in **ascending** order.
+pub(crate) fn k_smallest_general<I, F>(iter: I, k: usize, mut comparator: F) -> Vec<I::Item>
+where
+    I: Iterator,
+    F: FnMut(&I::Item, &I::Item) -> Ordering,
+{
+    /// Sift the element currently at `origin` away from the root until it is properly ordered.
+    ///
+    /// This will leave **larger** elements closer to the root of the heap.
+    fn sift_down<T, F>(heap: &mut [T], is_less_than: &mut F, mut origin: usize)
+    where
+        F: FnMut(&T, &T) -> bool,
+    {
+        #[inline]
+        fn children_of(n: usize) -> (usize, usize) {
+            (2 * n + 1, 2 * n + 2)
+        }
+
+        while origin < heap.len() {
+            let (left_idx, right_idx) = children_of(origin);
+            if left_idx >= heap.len() {
+                return;
+            }
+
+            let replacement_idx =
+                if right_idx < heap.len() && is_less_than(&heap[left_idx], &heap[right_idx]) {
+                    right_idx
+                } else {
+                    left_idx
+                };
+
+            if is_less_than(&heap[origin], &heap[replacement_idx]) {
+                heap.swap(origin, replacement_idx);
+                origin = replacement_idx;
+            } else {
+                return;
+            }
+        }
+    }
+
+    if k == 0 {
+        iter.last();
+        return Vec::new();
+    }
+    if k == 1 {
+        return iter.min_by(comparator).into_iter().collect();
+    }
+    let mut iter = iter.fuse();
+    let mut storage: Vec<I::Item> = iter.by_ref().take(k).collect();
+
+    let mut is_less_than = move |a: &_, b: &_| comparator(a, b) == Ordering::Less;
+
+    // Rearrange the storage into a valid heap by reordering from the second-bottom-most layer up to the root.
+    // Slightly faster than ordering on each insert, but only by a factor of lg(k).
+    // The resulting heap has the **largest** item on top.
+    for i in (0..=(storage.len() / 2)).rev() {
+        sift_down(&mut storage, &mut is_less_than, i);
+    }
+
+    iter.for_each(|val| {
+        debug_assert_eq!(storage.len(), k);
+        if is_less_than(&val, &storage[0]) {
+            // Treating this as an push-and-pop saves having to write a sift-up implementation.
+            // https://en.wikipedia.org/wiki/Binary_heap#Insert_then_extract
+            storage[0] = val;
+            // We retain the smallest items we've seen so far, but ordered largest first so we can drop the largest efficiently.
+            sift_down(&mut storage, &mut is_less_than, 0);
+        }
+    });
+
+    // Ultimately the items need to be in least-first, strict order, but the heap is currently largest-first.
+    // To achieve this, repeatedly,
+    // 1) "pop" the largest item off the heap into the tail slot of the underlying storage,
+    // 2) shrink the logical size of the heap by 1,
+    // 3) restore the heap property over the remaining items.
+    let mut heap = &mut storage[..];
+    while heap.len() > 1 {
+        let last_idx = heap.len() - 1;
+        heap.swap(0, last_idx);
+        // Sifting over a truncated slice means that the sifting will not disturb already popped elements.
+        heap = &mut heap[..last_idx];
+        sift_down(heap, &mut is_less_than, 0);
+    }
+
+    storage
+}
+
+pub(crate) fn k_smallest_relaxed_general<I, F>(iter: I, k: usize, mut comparator: F) -> Vec<I::Item>
+where
+    I: Iterator,
+    F: FnMut(&I::Item, &I::Item) -> Ordering,
+{
+    if k == 0 {
+        iter.last();
+        return Vec::new();
+    }
+
+    let mut iter = iter.fuse();
+    let mut buf = iter.by_ref().take(2 * k).collect::<Vec<_>>();
+
+    if buf.len() < k {
+        buf.sort_unstable_by(&mut comparator);
+        return buf;
+    }
+
+    buf.select_nth_unstable_by(k - 1, &mut comparator);
+    buf.truncate(k);
+
+    iter.for_each(|val| {
+        if comparator(&val, &buf[k - 1]) != Ordering::Less {
+            return;
+        }
+
+        assert_ne!(buf.len(), buf.capacity());
+        buf.push(val);
+
+        if buf.len() == 2 * k {
+            buf.select_nth_unstable_by(k - 1, &mut comparator);
+            buf.truncate(k);
+        }
+    });
+
+    buf.sort_unstable_by(&mut comparator);
+    buf.truncate(k);
+    buf
+}
+
+#[inline]
+pub(crate) fn key_to_cmp<T, K, F>(mut key: F) -> impl FnMut(&T, &T) -> Ordering
+where
+    F: FnMut(&T) -> K,
+    K: Ord,
+{
+    move |a, b| key(a).cmp(&key(b))
+}