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-rw-r--r--src/pkg/container/heap/heap.go117
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diff --git a/src/pkg/container/heap/heap.go b/src/pkg/container/heap/heap.go
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-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// 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.
-//
-package heap
-
-import "sort"
-
-// 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. To add and remove things from the heap,
-// use heap.Push and heap.Pop.
-type Interface interface {
- sort.Interface
- Push(x interface{}) // add x as element Len()
- Pop() interface{} // remove and return element Len() - 1.
-}
-
-// A heap must be initialized before any of the heap operations
-// can be used. Init is idempotent with respect to the heap invariants
-// and may be called whenever the heap invariants may have been invalidated.
-// Its complexity is O(n) where n = h.Len().
-//
-func Init(h Interface) {
- // heapify
- n := h.Len()
- for i := n/2 - 1; i >= 0; i-- {
- down(h, i, n)
- }
-}
-
-// Push pushes the element x onto the heap. The complexity is
-// O(log(n)) where n = h.Len().
-//
-func Push(h Interface, x interface{}) {
- h.Push(x)
- up(h, h.Len()-1)
-}
-
-// Pop removes the minimum element (according to Less) from the heap
-// and returns it. The complexity is O(log(n)) where n = h.Len().
-// It is equivalent to Remove(h, 0).
-//
-func Pop(h Interface) interface{} {
- n := h.Len() - 1
- h.Swap(0, n)
- down(h, 0, n)
- return h.Pop()
-}
-
-// Remove removes the element at index i from the heap.
-// The complexity is O(log(n)) where n = h.Len().
-//
-func Remove(h Interface, i int) interface{} {
- n := h.Len() - 1
- if n != i {
- h.Swap(i, n)
- down(h, i, n)
- up(h, i)
- }
- return h.Pop()
-}
-
-// 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 Fix(h Interface, i int) {
- down(h, i, h.Len())
- up(h, i)
-}
-
-func up(h Interface, j int) {
- for {
- i := (j - 1) / 2 // parent
- if i == j || !h.Less(j, i) {
- break
- }
- h.Swap(i, j)
- j = i
- }
-}
-
-func down(h Interface, i, n int) {
- for {
- j1 := 2*i + 1
- if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
- break
- }
- j := j1 // left child
- if j2 := j1 + 1; j2 < n && !h.Less(j1, j2) {
- j = j2 // = 2*i + 2 // right child
- }
- if !h.Less(j, i) {
- break
- }
- h.Swap(i, j)
- i = j
- }
-}