code: func (h *heapData) Swap(i, j int) {
  	h.queue[i], h.queue[j] = h.queue[j], h.queue[i]
  	item := h.items[h.queue[i]]
  	item.index = i
  	item = h.items[h.queue[j]]
  	item.index = j
  }
docs: // Swap implements swapping of two elements in the heap. This is a part of standard
  // heap interface and should never be called directly.