94 lines
2.6 KiB
Go
94 lines
2.6 KiB
Go
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// Copyright 2020 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package s2
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import "container/heap"
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// A queryQueueEntry stores CellIDs and distance from a target. It is used by the
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// different S2 Query types to efficiently build their internal priority queue
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// in the optimized algorithm implementations.
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type queryQueueEntry struct {
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// A lower bound on the distance from the target to ID. This is the key
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// of the priority queue.
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distance distance
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// The cell being queued.
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id CellID
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// If the CellID belongs to a ShapeIndex, this field stores the
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// corresponding ShapeIndexCell. Otherwise ID is a proper ancestor of
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// one or more ShapeIndexCells and this field stores is nil.
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indexCell *ShapeIndexCell
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}
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// queryQueue is used by the optimized algorithm to maintain a priority queue of
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// unprocessed CellIDs, sorted in increasing order of distance from the target.
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type queryQueue struct {
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queue queryPQ
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}
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// newQueryQueue returns a new initialized queryQueue.
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func newQueryQueue() *queryQueue {
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q := &queryQueue{
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queue: make(queryPQ, 0),
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}
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heap.Init(&q.queue)
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return q
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}
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// push adds the given entry to the top of this queue.
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func (q *queryQueue) push(e *queryQueueEntry) {
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heap.Push(&q.queue, e)
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}
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// pop returns the top element of this queue.
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func (q *queryQueue) pop() *queryQueueEntry {
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return heap.Pop(&q.queue).(*queryQueueEntry)
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}
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func (q *queryQueue) size() int {
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return q.queue.Len()
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}
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func (q *queryQueue) reset() {
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q.queue = q.queue[:0]
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}
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// queryPQ is a priority queue that implements the heap interface.
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type queryPQ []*queryQueueEntry
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func (q queryPQ) Len() int { return len(q) }
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func (q queryPQ) Less(i, j int) bool {
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return q[i].distance.less(q[j].distance)
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}
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// Swap swaps the two entries.
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func (q queryPQ) Swap(i, j int) {
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q[i], q[j] = q[j], q[i]
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}
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// Push adds the given entry to the queue.
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func (q *queryPQ) Push(x interface{}) {
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item := x.(*queryQueueEntry)
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*q = append(*q, item)
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}
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// Pop returns the top element of the queue.
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func (q *queryPQ) Pop() interface{} {
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item := (*q)[len(*q)-1]
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*q = (*q)[:len(*q)-1]
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return item
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}
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