// CookieJar - A contestant's algorithm toolbox
// Copyright (c) 2013 Peter Szilagyi. All rights reserved.
//
// CookieJar is dual licensed: use of this source code is governed by a BSD
// license that can be found in the LICENSE file. Alternatively, the CookieJar
// toolbox may be used in accordance with the terms and conditions contained
// in a signed written agreement between you and the author(s).
// This is a duplicated and slightly modified version of "gopkg.in/karalabe/cookiejar.v2/collections/prque".
package prque
// The size of a block of data
const blockSize = 4096
// A prioritized item in the sorted stack.
//
// Note: priorities can "wrap around" the int64 range, a comes before b if (a.priority - b.priority) > 0.
// The difference between the lowest and highest priorities in the queue at any point should be less than 2^63.
type item struct {
value interface{}
priority int64
}
// SetIndexCallback is called when the element is moved to a new index.
// Providing SetIndexCallback is optional, it is needed only if the application needs
// to delete elements other than the top one.
type SetIndexCallback func(data interface{}, index int)
// Internal sortable stack data structure. Implements the Push and Pop ops for
// the stack (heap) functionality and the Len, Less and Swap methods for the
// sortability requirements of the heaps.
type sstack struct {
setIndex SetIndexCallback
size int
capacity int
offset int
blocks [][]*item
active []*item
}
// Creates a new, empty stack.
func newSstack(setIndex SetIndexCallback) *sstack {
result := new(sstack)
result.setIndex = setIndex
result.active = make([]*item, blockSize)
result.blocks = [][]*item{result.active}
result.capacity = blockSize
return result
}
// Pushes a value onto the stack, expanding it if necessary. Required by
// heap.Interface.
func (s *sstack) Push(data interface{}) {
if s.size == s.capacity {
s.active = make([]*item, blockSize)
s.blocks = append(s.blocks, s.active)
s.capacity += blockSize
s.offset = 0
} else if s.offset == blockSize {
s.active = s.blocks[s.size/blockSize]
s.offset = 0
}
if s.setIndex != nil {
s.setIndex(data.(*item).value, s.size)
}
s.active[s.offset] = data.(*item)
s.offset++
s.size++
}
// Pops a value off the stack and returns it. Currently no shrinking is done.
// Required by heap.Interface.
func (s *sstack) Pop() (res interface{}) {
s.size--
s.offset--
if s.offset < 0 {
s.offset = blockSize - 1
s.active = s.blocks[s.size/blockSize]
}
res, s.active[s.offset] = s.active[s.offset], nil
if s.setIndex != nil {
s.setIndex(res.(*item).value, -1)
}
return
}
// Returns the length of the stack. Required by sort.Interface.
func (s *sstack) Len() int {
return s.size
}
// Compares the priority of two elements of the stack (higher is first).
// Required by sort.Interface.
func (s *sstack) Less(i, j int) bool {
return (s.blocks[i/blockSize][i%blockSize].priority - s.blocks[j/blockSize][j%blockSize].priority) > 0
}
// Swaps two elements in the stack. Required by sort.Interface.
func (s *sstack) Swap(i, j int) {
ib, io, jb, jo := i/blockSize, i%blockSize, j/blockSize, j%blockSize
a, b := s.blocks[jb][jo], s.blocks[ib][io]
if s.setIndex != nil {
s.setIndex(a.value, i)
s.setIndex(b.value, j)
}
s.blocks[ib][io], s.blocks[jb][jo] = a, b
}
// Resets the stack, effectively clearing its contents.
func (s *sstack) Reset() {
*s = *newSstack(s.setIndex)
}
