gtsocial-umbx

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query_entry.go (2643B)

      1 // Copyright 2020 Google Inc. All rights reserved.
      2 //
      3 // Licensed under the Apache License, Version 2.0 (the "License");
      4 // you may not use this file except in compliance with the License.
      5 // You may obtain a copy of the License at
      6 //
      7 //     http://www.apache.org/licenses/LICENSE-2.0
      8 //
      9 // Unless required by applicable law or agreed to in writing, software
     10 // distributed under the License is distributed on an "AS IS" BASIS,
     11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     12 // See the License for the specific language governing permissions and
     13 // limitations under the License.
     14 
     15 package s2
     16 
     17 import "container/heap"
     18 
     19 // A queryQueueEntry stores CellIDs and distance from a target. It is used by the
     20 // different S2 Query types to efficiently build their internal priority queue
     21 // in the optimized algorithm implementations.
     22 type queryQueueEntry struct {
     23 	// A lower bound on the distance from the target to ID. This is the key
     24 	// of the priority queue.
     25 	distance distance
     26 
     27 	// The cell being queued.
     28 	id CellID
     29 
     30 	// If the CellID belongs to a ShapeIndex, this field stores the
     31 	// corresponding ShapeIndexCell. Otherwise ID is a proper ancestor of
     32 	// one or more ShapeIndexCells and this field stores is nil.
     33 	indexCell *ShapeIndexCell
     34 }
     35 
     36 // queryQueue is used by the optimized algorithm to maintain a priority queue of
     37 // unprocessed CellIDs, sorted in increasing order of distance from the target.
     38 type queryQueue struct {
     39 	queue queryPQ
     40 }
     41 
     42 // newQueryQueue returns a new initialized queryQueue.
     43 func newQueryQueue() *queryQueue {
     44 	q := &queryQueue{
     45 		queue: make(queryPQ, 0),
     46 	}
     47 	heap.Init(&q.queue)
     48 	return q
     49 }
     50 
     51 // push adds the given entry to the top of this queue.
     52 func (q *queryQueue) push(e *queryQueueEntry) {
     53 	heap.Push(&q.queue, e)
     54 }
     55 
     56 // pop returns the top element of this queue.
     57 func (q *queryQueue) pop() *queryQueueEntry {
     58 	return heap.Pop(&q.queue).(*queryQueueEntry)
     59 }
     60 
     61 func (q *queryQueue) size() int {
     62 	return q.queue.Len()
     63 }
     64 
     65 func (q *queryQueue) reset() {
     66 	q.queue = q.queue[:0]
     67 }
     68 
     69 // queryPQ is a priority queue that implements the heap interface.
     70 type queryPQ []*queryQueueEntry
     71 
     72 func (q queryPQ) Len() int { return len(q) }
     73 func (q queryPQ) Less(i, j int) bool {
     74 	return q[i].distance.less(q[j].distance)
     75 }
     76 
     77 // Swap swaps the two entries.
     78 func (q queryPQ) Swap(i, j int) {
     79 	q[i], q[j] = q[j], q[i]
     80 }
     81 
     82 // Push adds the given entry to the queue.
     83 func (q *queryPQ) Push(x interface{}) {
     84 	item := x.(*queryQueueEntry)
     85 	*q = append(*q, item)
     86 }
     87 
     88 // Pop returns the top element of the queue.
     89 func (q *queryPQ) Pop() interface{} {
     90 	item := (*q)[len(*q)-1]
     91 	*q = (*q)[:len(*q)-1]
     92 	return item
     93 }