java 有向加权图的邻接表

adjacency list of a directed weighted graph

提问by denchr

I am using adjacency lists to represent a directed weighted graph and based on the example code provided by thisSO question, I have created the following:

我正在使用邻接列表来表示有向加权图，并基于此SO 问题提供的示例代码，我创建了以下内容：

import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

public class _Graph {
    private Map<String, LinkedHashSet<HashMap<String, Integer>>> map = new HashMap<String, LinkedHashSet<HashMap<String, Integer>>>();

    public void addEdge(String node1, String node2, int dist) {
        LinkedHashSet<HashMap<String, Integer>> adjacent = map.get(node1);
        HashMap<String, Integer> innerMap = new HashMap<String, Integer>();
        if(adjacent==null) {
            adjacent = new LinkedHashSet<HashMap<String, Integer>>();                       
            map.put(node1, adjacent);
        }
        innerMap.put(node2, dist);
        adjacent.add(innerMap);
    }

    public boolean isConnected(String node1, String node2) {
        Set<HashMap<String, Integer>> adjacent = map.get(node1);
        if(adjacent==null) {
            return false;
        }
        return adjacent.contains(node2);
    }

    public LinkedList<HashMap<String, Integer>> adjacentNodes(String node) {
        LinkedHashSet<HashMap<String, Integer>> adjacent = map.get(node);
        if(adjacent==null) {
            return new LinkedList<HashMap<String, Integer>>();
        }
        return new LinkedList<HashMap<String, Integer>>(adjacent);
    }

}

I am having trouble making the isConnectedmethod to work properly. Am I using a wrong data structure to represent the graph here (Map<String, LinkedHashSet<HashMap<String, Integer>>>)? The hashmap will hold the name of the connected node and the distance to it:

我无法使该isConnected方法正常工作。我是否使用错误的数据结构来表示此处的图形 ( Map<String, LinkedHashSet<HashMap<String, Integer>>>)？hashmap 将保存连接节点的名称和到它的距离：

Map<startNode, LinkedHashSet<HashMap<endNode, distanceToEndNode>>>

1. Basically how can I check if a node belongs to the adjacency list of a given base node? I think the problem is reduced to iterating properly over the adjacentSet<HashMap<String, Integer>>structure, or is my reasoning wrong?
2. In my second method adjacentNodes(String node)I am returning a linked list containing the maps (in a set structure) of the connected nodes and their distances. How could I efficiently iterate to see all connections of a any given node?

1. 基本上如何检查节点是否属于给定基节点的邻接列表？我认为问题归结为在adjacentSet<HashMap<String, Integer>>结构上正确迭代，还是我的推理错误？
2. 在我的第二种方法中， adjacentNodes(String node)我返回一个链表，其中包含连接节点的地图（在一个集合结构中）及其距离。我如何有效地迭代以查看任何给定节点的所有连接？

回答by Keith Randall

I think LinkedHashSetis not needed here, you can represent the graph with just a Map<String, Map<String, Integer>>.

我认为LinkedHashSet这里不需要，您可以只用一个Map<String, Map<String, Integer>>.

isConnectedis basically what you already have:

isConnected基本上是你已经拥有的：

public boolean isConnected(String node1, String node2) {
    Map<String, Integer> adjacent = map.get(node1);
    if(adjacent==null) {
        return false;
    }
    return adjacent.containsKey(node2);
}

adjacentNodesjust needs to pull out the entries in the hash set for the source node

adjacentNodes只需要为源节点提取哈希集中的条目

public Collection<Map.Entry<String, Integer>> adjacentNodes(String node) {
    Map<String, Integer> adjacent = map.get(node);
    if(adjacent==null) {
        return new ArrayList<Map.Entry<String, Integer>>();
    }
    return adjacent.entrySet();
}