Top-K with a bounded min-heap

type minInts []int

func (h minInts) Len() int           { return len(h) }
func (h minInts) Less(i, j int) bool { return h[i] < h[j] }
func (h minInts) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *minInts) Push(x any)        { *h = append(*h, x.(int)) }
func (h *minInts) Pop() any {
	old := *h
	x := old[len(old)-1]
	*h = old[:len(old)-1]
	return x
}

// Requires imports container/heap and sort.
func TopK(xs []int, k int) []int {
	if k <= 0 {
		return nil
	}
	h := &minInts{}
	for _, x := range xs {
		if h.Len() < k {
			heap.Push(h, x)
		} else if x > (*h)[0] {
			(*h)[0] = x
			heap.Fix(h, 0)
		}
	}
	out := append([]int(nil), (*h)...)
	sort.Ints(out)
	return out
}