ARAstar算法的Java实现

ARA*（Anytime Repairing A*）算法是一种基于A*算法的增量式搜索算法，可以在有限时间内找到最优解或者近似最优解。下面是ARA*算法的Java实现：

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Set;

public class ARAStar {
    private static final int INFINITY = Integer.MAX_VALUE;
    private static final double EPSILON = 1.0;

    private final List<Node> nodes;
    private final Map<Node, Integer> gScore;
    private final Map<Node, Integer> rhsScore;
    private final Set<Node> openSet;
    private final Set<Node> closedSet;
    private final PriorityQueue<Node> queue;

    private final Node start;
    private final Node goal;

    public ARAStar(List<Node> nodes, Node start, Node goal) {
        this.nodes = nodes;
        this.start = start;
        this.goal = goal;

        gScore = new HashMap<>();
        rhsScore = new HashMap<>();
        openSet = new HashSet<>();
        closedSet = new HashSet<>();
        queue = new PriorityQueue<>(Comparator.comparingDouble(this::getKey));

        for (Node node : nodes) {
            gScore.put(node, INFINITY);
            rhsScore.put(node, INFINITY);
        }

        rhsScore.put(goal, 0);
        queue.add(goal);
    }

    public List<Node> search() {
        double minKey = 0.0;
        while (!openSet.isEmpty() || rhsScore.get(start) > gScore.get(start)) {
            if (openSet.isEmpty()) {
                computePath(minKey);
            }

            Node current = queue.poll();
            openSet.remove(current);

            if (gScore.get(current) > rhsScore.get(current)) {
                gScore.put(current, rhsScore.get(current));
                for (Node neighbor : current.getNeighbors()) {
                    updateNode(neighbor);
                }
            } else {
                gScore.put(current, INFINITY);
                for (Node neighbor : current.getNeighbors()) {
                    updateNode(neighbor);
                }
                updateNode(current);
            }

            if (rhsScore.get(start) < INFINITY && !openSet.isEmpty()) {
                minKey = getKey(openSet.iterator().next());
            }
        }

        List<Node> path = new ArrayList<>();
        Node current = start;
        path.add(current);
        while (!current.equals(goal)) {
            current = current.getBestSuccessor();
            path.add(current);
        }
        return path;
    }

    private void computePath(double minKey) {
        while (true) {
            Node current = queue.peek();
            if (current == null || getKey(current) >= minKey) {
                break;
            }
            queue.poll();
            openSet.remove(current);
            closedSet.add(current);

            for (Node neighbor : current.getNeighbors()) {
                if (!closedSet.contains(neighbor)) {
                    updateNode(neighbor);
                }
            }
        }
    }

    private void updateNode(Node node) {
        if (!node.equals(goal)) {
            int minScore = INFINITY;
            for (Node successor : node.getNeighbors()) {
                int score = gScore.get(successor) + successor.getCost(node);
                minScore = Math.min(minScore, score);
            }
            rhsScore.put(node, minScore);
        }

        if (openSet.contains(node)) {
            queue.remove(node);
        }

        if (gScore.get(node) != rhsScore.get(node)) {
            queue.add(node);
            openSet.add(node);
        }
    }

    private double getKey(Node node) {
        return Math.min(gScore.get(node), rhsScore.get(node) + EPSILON * node.getHeuristic(goal));
    }
}

其中，Node类表示图中的节点，包括节点编号、节点到起点的距离、节点到终点的距离以及节点的邻居节点。search方法实现了ARA*算法的主要逻辑，computePath方法用于计算路径，updateNode方法用于更新节点的rhs值和g值，getKey方法用于计算节点的f值。

可以根据具体的问题来实现Node类和计算节点到终点距离的heuristic函数。