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/
astar.go
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/
astar.go
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// code of this file is a modified version of code from
// github.com/beefsack/go-astar, which has the following license:
//
// Copyright (c) 2014 Michael Charles Alexander
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
package main
import (
"container/heap"
)
type node struct {
Pos position
Cost int
Rank int
Parent *position
Open bool
Closed bool
Index int
Num int
}
type nodeMap map[position]*node
var nodeCache []node
func init() {
nodeCache = make([]node, 0, DungeonNCells)
}
func (nm nodeMap) get(p position) *node {
n, ok := nm[p]
if !ok {
nodeCache = append(nodeCache, node{Pos: p})
n = &nodeCache[len(nodeCache)-1]
nm[p] = n
}
return n
}
type Astar interface {
Neighbors(position) []position
Cost(position, position) int
Estimation(position, position) int
}
func AstarPath(ast Astar, from, to position) (path []position, length int, found bool) {
nodeCache = nodeCache[:0]
nm := nodeMap{}
nq := &priorityQueue{}
heap.Init(nq)
fromNode := nm.get(from)
fromNode.Open = true
num := 0
fromNode.Num = num
heap.Push(nq, fromNode)
for {
if nq.Len() == 0 {
// There's no path, return found false.
return
}
current := heap.Pop(nq).(*node)
current.Open = false
current.Closed = true
if current.Pos == to {
// Found a path to the goal.
p := []position{}
curr := current
for {
p = append(p, curr.Pos)
if curr.Parent == nil {
break
}
curr = nm[*curr.Parent]
}
return p, current.Cost, true
}
for _, neighbor := range ast.Neighbors(current.Pos) {
cost := current.Cost + ast.Cost(current.Pos, neighbor)
neighborNode := nm.get(neighbor)
if cost < neighborNode.Cost {
if neighborNode.Open {
heap.Remove(nq, neighborNode.Index)
}
neighborNode.Open = false
neighborNode.Closed = false
}
if !neighborNode.Open && !neighborNode.Closed {
neighborNode.Cost = cost
neighborNode.Open = true
neighborNode.Rank = cost + ast.Estimation(neighbor, to)
neighborNode.Parent = ¤t.Pos
num++
neighborNode.Num = num
heap.Push(nq, neighborNode)
}
}
}
}
// A priorityQueue implements heap.Interface and holds Nodes. The
// priorityQueue is used to track open nodes by rank.
type priorityQueue []*node
func (pq priorityQueue) Len() int {
return len(pq)
}
func (pq priorityQueue) Less(i, j int) bool {
//return pq[i].Rank < pq[j].Rank
return pq[i].Rank < pq[j].Rank || pq[i].Rank == pq[j].Rank && pq[i].Num < pq[j].Num
}
func (pq priorityQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].Index = i
pq[j].Index = j
}
func (pq *priorityQueue) Push(x interface{}) {
n := len(*pq)
no := x.(*node)
no.Index = n
*pq = append(*pq, no)
}
func (pq *priorityQueue) Pop() interface{} {
old := *pq
n := len(old)
no := old[n-1]
no.Index = -1
*pq = old[0 : n-1]
return no
}