Fix re-establishes the heap ordering after the element at index i has changed its value.

A heap must be initialized before any of the heap operations can be used.

Pop removes the minimum element (according to Less) from the heap and returns it.

Push pushes the element x onto the heap.

Remove removes the element at index i from the heap.

Any type that implements heap.Interface may be used as a min-heap with the following invariants (established after Init has been called or if the data is empty or sorted): !h.Less(j, i) for 0 <= i < h.Len() and 2*i+1 <= j <= 2*i+2 and j < h.Len() Note that Push and Pop in this interface are for package heap's implementation to call.