92 lines
2.5 KiB
Go
92 lines
2.5 KiB
Go
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// CookieJar - A contestant's algorithm toolbox
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// Copyright (c) 2013 Peter Szilagyi. All rights reserved.
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//
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// CookieJar is dual licensed: use of this source code is governed by a BSD
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// license that can be found in the LICENSE file. Alternatively, the CookieJar
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// toolbox may be used in accordance with the terms and conditions contained
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// in a signed written agreement between you and the author(s).
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package prque
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// The size of a block of data
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const blockSize = 4096
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// A prioritized item in the sorted stack.
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type item struct {
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value interface{}
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priority float32
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}
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// Internal sortable stack data structure. Implements the Push and Pop ops for
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// the stack (heap) functionality and the Len, Less and Swap methods for the
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// sortability requirements of the heaps.
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type sstack struct {
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size int
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capacity int
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offset int
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blocks [][]*item
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active []*item
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}
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// Creates a new, empty stack.
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func newSstack() *sstack {
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result := new(sstack)
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result.active = make([]*item, blockSize)
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result.blocks = [][]*item{result.active}
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result.capacity = blockSize
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return result
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}
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// Pushes a value onto the stack, expanding it if necessary. Required by
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// heap.Interface.
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func (s *sstack) Push(data interface{}) {
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if s.size == s.capacity {
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s.active = make([]*item, blockSize)
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s.blocks = append(s.blocks, s.active)
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s.capacity += blockSize
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s.offset = 0
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} else if s.offset == blockSize {
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s.active = s.blocks[s.size/blockSize]
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s.offset = 0
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}
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s.active[s.offset] = data.(*item)
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s.offset++
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s.size++
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}
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// Pops a value off the stack and returns it. Currently no shrinking is done.
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// Required by heap.Interface.
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func (s *sstack) Pop() (res interface{}) {
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s.size--
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s.offset--
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if s.offset < 0 {
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s.offset = blockSize - 1
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s.active = s.blocks[s.size/blockSize]
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}
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res, s.active[s.offset] = s.active[s.offset], nil
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return
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}
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// Returns the length of the stack. Required by sort.Interface.
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func (s *sstack) Len() int {
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return s.size
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}
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// Compares the priority of two elements of the stack (higher is first).
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// Required by sort.Interface.
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func (s *sstack) Less(i, j int) bool {
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return s.blocks[i/blockSize][i%blockSize].priority > s.blocks[j/blockSize][j%blockSize].priority
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}
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// Swaps two elements in the stack. Required by sort.Interface.
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func (s *sstack) Swap(i, j int) {
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ib, io, jb, jo := i/blockSize, i%blockSize, j/blockSize, j%blockSize
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s.blocks[ib][io], s.blocks[jb][jo] = s.blocks[jb][jo], s.blocks[ib][io]
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}
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// Resets the stack, effectively clearing its contents.
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func (s *sstack) Reset() {
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*s = *newSstack()
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}
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