Java利用Dijkstra算法求解拓扑关系最短路径

 
import com.gis.spacedata.domain.entity.tunnel.TunnelTopologyRelEntity;
import lombok.extern.slf4j.Slf4j;
 
import java.util.*;
 
@Slf4j
public class PathUtil {
 
 
    /**
     * 方法描述: 求最短路径
     *
     */
    public static List<Long> dijkstra(List<TunnelTopologyRelEntity> topologies, long start, long end) {
        int size=topologies.size();
        Map<String, Double> distMap = new HashMap<>(size);
        //存放源节点到各个节点的距离key 目标节点，value 源节点到该节点的距离
        Map<Long, Double> dists = new HashMap<>(size);
        //key: 当前节点，value：从原点到达key的最短路径的前驱（上一个）节点
        Map<Long, Long> parent = new HashMap<>(size);
        //被标记最短距离的节点
        Set<Long> markNodes = new HashSet<>(size);
        //获取所有节点列表
        Set<Long> nodes = new HashSet<>(10);
        for (TunnelTopologyRelEntity e : topologies) {
            nodes.add(e.getSource());
            nodes.add(e.getTarget());
            distMap.put(e.getSource()   "-"   e.getTarget(), e.getCost());
        }
        //初始化各个节点到源节点的距离
        for (long node : nodes) {
            if (node == start) {
                dists.put(node, 0d);
            } else {
                dists.put(node, getCost(distMap, start, node));
            }
        }
        // 不断迭代
        while (true) {
            //距离源节点距离最近的节点(还未被标记为离源节点最近的点)
            long closestNode = -1;
            double min = Double.MAX_VALUE;
            for (Map.Entry<Long, Double> entry : dists.entrySet()) {
                if (entry.getValue() < min && !markNodes.contains(entry.getKey())) {
                    min = entry.getValue();
                    closestNode = entry.getKey();
                }
            }
            // 找不到可达的路径了或到达目标点
            if (closestNode == -1 || closestNode==end) {
                break;
            }
            markNodes.add(closestNode);
            for (long node : nodes) {
                double dist = getCost(distMap, closestNode, node);
                // 找到一个为扩展的子节点
                if (dist > 0 && !markNodes.contains(node)) {
                    double new_dist = dists.get(closestNode)   dist;
                    // 新距离小于原始距离，更新
                    if (new_dist < dists.get(node)) {
                        dists.put(node, new_dist);
                        parent.put(node, closestNode);
                    }
                }
            }
        }
        // 倒叙查找到路径
        if (dists.get(end) == Integer.MAX_VALUE) {
            log.info(start   "到"   end   "之间没有最短路径");
            return null;
        } else {
            List<Long> path = new ArrayList<>();
            long current = end;
            path.add(current);
            while (current != start) {
                current = parent.get(current);
                path.add(current);
            }
            //反转
            Collections.reverse(path);
            return path;
        }
    }
 
    /**
     * 方法描述: 获取相邻节点之间距离
     *
     */
    private static double getCost(Map<String, Double> distMap, long start, long end) {
        if (start == end) {
            return 0;
        }
        Double dist1 = distMap.get(start   "-"   end);
        if (dist1 != null) {
            return dist1;
        }
        Double dist2 = distMap.get(end   "-"   start);
        if (dist2 != null) {
            return dist2;
        }
        return Double.MAX_VALUE;
    }
 
 
}

public List<Long> getPointShortWay(String startCode, String endCode) {
        TunnelTopologyCodeRelEntity startTopologyCodeRel = getTopologyCodeRel(startCode);
        TunnelTopologyCodeRelEntity endTopologyCodeRel = getTopologyCodeRel(endCode);
        if (Func.isNull(startTopologyCodeRel) || Func.isNull(endTopologyCodeRel)) {
            return Collections.emptyList();
        }
        List<TunnelTopologyRelEntity> list=list();
        return PathUtil.dijkstra(list,startTopologyCodeRel.getId(), endTopologyCodeRel.getId());
    }