用java实现一个重用搜索结果的ARAstar算法
时间: 2023-07-14 09:13:04 浏览: 91
ARA*算法是A*算法的一个变体,它可以通过调整启发式函数的权重来控制搜索的速度和准确性。重用搜索结果是一种优化技巧,可以在重复搜索相同的状态时节省计算资源。下面是用Java实现重用搜索结果的ARA*算法的代码示例:
```
import java.util.*;
public class ARAStar {
// 路径节点类
private class Node implements Comparable<Node> {
int x, y; // 节点坐标
double g, h, f; // 路径长度、启发函数值、路径估价函数值
Node parent; // 父节点
public Node(int x, int y, double g, double h, Node parent) {
this.x = x;
this.y = y;
this.g = g;
this.h = h;
this.f = g + h;
this.parent = parent;
}
public int compareTo(Node other) {
return Double.compare(this.f, other.f);
}
}
private int[][] map; // 地图
private int startX, startY; // 起点坐标
private int targetX, targetY; // 终点坐标
private double weight; // 启发函数权重
private PriorityQueue<Node> openList; // 优先队列
private Map<String, Node> closedList; // 关闭列表
public ARAStar(int[][] map, int startX, int startY, int targetX, int targetY, double weight) {
this.map = map;
this.startX = startX;
this.startY = startY;
this.targetX = targetX;
this.targetY = targetY;
this.weight = weight;
this.openList = new PriorityQueue<>();
this.closedList = new HashMap<>();
}
// 启发函数
private double heuristic(int x, int y) {
return Math.sqrt(Math.pow(x - targetX, 2) + Math.pow(y - targetY, 2));
}
// A*算法
private Node astar(double threshold) {
Node startNode = new Node(startX, startY, 0, heuristic(startX, startY), null);
openList.add(startNode);
while (!openList.isEmpty()) {
Node currentNode = openList.poll();
if (currentNode.x == targetX && currentNode.y == targetY) {
return currentNode;
}
String key = currentNode.x + "," + currentNode.y;
if (closedList.containsKey(key)) {
Node savedNode = closedList.get(key);
if (currentNode.g < savedNode.g) {
closedList.remove(key);
} else {
continue;
}
}
closedList.put(key, currentNode);
for (int dx = -1; dx <= 1; dx++) {
for (int dy = -1; dy <= 1; dy++) {
if (dx == 0 && dy == 0) continue;
int nextX = currentNode.x + dx;
int nextY = currentNode.y + dy;
if (nextX < 0 || nextX >= map.length || nextY < 0 || nextY >= map[0].length) continue;
if (map[nextX][nextY] == 1) continue;
double g = currentNode.g + Math.sqrt(dx * dx + dy * dy);
double h = heuristic(nextX, nextY) * weight;
double f = g + h;
Node nextNode = new Node(nextX, nextY, g, h, currentNode);
if (f <= threshold) {
openList.add(nextNode);
}
}
}
}
return null;
}
// ARA*算法
public List<Node> search() {
double threshold = heuristic(startX, startY) * weight;
Node goalNode = astar(threshold);
while (goalNode == null) {
threshold *= 2;
goalNode = astar(threshold);
}
List<Node> path = new ArrayList<>();
while (goalNode != null) {
path.add(goalNode);
goalNode = goalNode.parent;
}
Collections.reverse(path);
return path;
}
}
```
在这个实现中,我们定义了一个`Node`类来表示路径节点,它包含了节点的坐标、路径长度、启发函数值、路径估价函数值和父节点。我们还定义了`heuristic`方法来计算启发函数值,`astar`方法来执行一次A*搜索,`search`方法来执行ARA*算法并返回最佳路径。在ARA*算法中,我们先执行一次A*搜索,然后通过不断增加阈值来重复执行A*搜索直到找到最佳路径。在每次A*搜索中,我们使用优先队列来维护待扩展的节点,使用HashMap来维护已扩展的节点,并且在需要重新扩展节点时进行重用。
要使用ARA*算法来搜索路径,我们可以创建一个`ARAStar`对象,并调用`search`方法来获取最佳路径。下面是一个使用示例:
```
int[][] map = {
{0, 0, 0, 0, 0},
{0, 1, 1, 1, 0},
{0, 0, 0, 0, 0},
{0, 1, 0, 1, 0},
{0, 0, 0, 0, 0},
};
int startX = 0, startY = 0, targetX = 4, targetY = 4;
double weight = 1.0;
ARAStar astar = new ARAStar(map, startX, startY, targetX, targetY, weight);
List<ARAStar.Node> path = astar.search();
for (ARAStar.Node node : path) {
System.out.println(node.x + "," + node.y);
}
```
在这个示例中,我们创建了一个5x5的地图,其中0表示可通过的区域,1表示障碍物。我们从起点(0,0)开始,朝着终点(4,4)搜索路径。我们设置启发函数权重为1.0,表示完全依赖启发函数。最后,我们打印出找到的路径节点的坐标。
阅读全文