heap

README

Generic Heap

This is a LITERAL COPY from the Go standard library because there is not yet a genric version of the containers/heap module in the Go 1.18 beta 1 release. I am sure this will come out in Go 1.18 or in a subsequent release shortly thereafter. This library is meant to be a bridge until that is done and nothing more.

Please do not use this for anything outside the lazylru module because it will be deleted as soon as a generic heap is available in the stardard library.

Documentation

Overview

Package heap provides heap operations for any type that implements heap.Interface. A heap is a tree with the property that each node is the minimum-valued node in its subtree.

The minimum element in the tree is the root, at index 0.

A heap is a common way to implement a priority queue. To build a priority queue, implement the Heap interface with the (negative) priority as the ordering for the Less method, so Push adds items while Pop removes the highest-priority item from the queue. The Examples include such an implementation; the file example_pq_test.go has the complete source.

Index

• func Fix[T any](h Interface[T], i int)
• func Init[T any](h Interface[T])
• func Pop[T any](h Interface[T]) T
• func Push[T any](h Interface[T], x T)
• func Remove[T any](h Interface[T], i int) T
• type Interface

Functions

func Fix

func Fix[T any](h Interface[T], i int)

Fix re-establishes the heap ordering after the element at index i has changed its value. Changing the value of the element at index i and then calling Fix is equivalent to, but less expensive than, calling Remove(h, i) followed by a Push of the new value. The complexity is O(log n) where n = h.Len().

func Init

func Init[T any](h Interface[T])

Init establishes the heap invariants required by the other routines in this package. Init is idempotent with respect to the heap invariants and may be called whenever the heap invariants may have been invalidated. The complexity is O(n) where n = h.Len().

func Pop

func Pop[T any](h Interface[T]) T

Pop removes and returns the minimum element (according to Less) from the heap. The complexity is O(log n) where n = h.Len(). Pop is equivalent to Remove(h, 0).

func Push

func Push[T any](h Interface[T], x T)

Push pushes the element x onto the heap. The complexity is O(log n) where n = h.Len().

func Remove

func Remove[T any](h Interface[T], i int) T

Remove removes and returns the element at index i from the heap. The complexity is O(log n) where n = h.Len().

Types

type Interface

type Interface[T any] interface {
	sort.Interface
	Push(x T) // add x as element Len()
	Pop() T   // remove and return element Len() - 1.
}

The Interface type describes the requirements for a type using the routines in this package. Any type that implements it 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. To add and remove things from the heap, use heap.Push and heap.Pop.