使用哈希图表示加权图

Question

My input text file:

  122334 
  45   
  67

Output should be:

0-{1=2,2=3,3=4} //node 0 is connected to 1 with weight 2,to 2 with weight 3,etc

1-{4=5}

2-{6=7}

Below is my program:

public class BFS {

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub

        HashMap<Integer, HashMap<Integer, Integer>>hash1=new HashMap<Integer,     HashMap<Integer,Integer>>();
        HashMap<Integer, Integer>hash2=new HashMap<Integer, Integer>();
        HashMap<Integer, Integer>temp1=new HashMap<Integer, Integer>();
    BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\Translab\\workspace\\Algorithms\\inputfile.txt"));
        int remainder,remainder2,j=0;
        int line=1;
        String str;
        while ((str =in.readLine()) != null) {
            int foo = Integer.parseInt(str);
          while(foo>0){
                 remainder=foo % 10;
                   foo = foo / 10;
                 remainder2=foo%10;
                 foo=foo/10;
                 temp1.put(remainder2, remainder);
                 hash2.putAll(temp1);

        }
        temp1.clear();
        hash1.put(j, hash2);

        j++;


        }
        for (Entry<Integer, HashMap<Integer, Integer>> entry  : hash1.entrySet()) {
            System.out.println(entry.getKey()+"-"+entry.getValue() );

        }
        in.close();
    }
}

With this am getting:

0-{1=2, 2=3, 3=4, 4=5, 6=7}

1-{1=2, 2=3, 3=4, 4=5, 6=7}

2-{1=2, 2=3, 3=4, 4=5, 6=7}

Can some one please help me-am new to hashmap.

Answer 1

You are unnecessarily overloading Map and Integer classes. Much better would be to encapsulate your graph nodes and edges in classes - this will make things much easier once you start having to perform operations on the graph:

class Node {
    private int id;
    private List<Edge> edges;
    public boolean hasId(int id) {
        return id == this.id;
    }
    public addEdge(Node node, int weight) {
        edges.add(new Edge(node, weight));
    }
}

class Edge {
    private int weight;
    private Node destination;
}

class Graph {
    private List<Node> nodes;
    public Node getNodeById(int id) {
        return nodes.stream()
            .filter(node -> node.hasId(id))
            .findFirst().orElse(null);
    }
}

I would also suggest that you break your input lines into tokens before the conversion to id and weight. This could be done inside the Graph class:

public void addEdge(int fromNodeID, String edgeData) {
    Node node = getNodeByID(fromNodeID);
    for (int pos = 0; pos < edgeData.length(); pos += 2) {
        int destNodeID = Integer.parseInt(edgeData.substring(pos, pos+1));
        int weight = Integer.parseInt(edgeData.substring(pos + 1, pos + 2);
        node.addEdge(getNodeByID(destNodeID), weight);
    }
}

Then processing input is fairly simple:

int id = 0;
Map<Integer, String> edgeData = new HashMap<>();
while((line = in.readLine()) != null) {
    graph.addNode(new Node(id));
    put(id, line);
}
edgeData.entrySet().stream()
    .forEach(entry -> graph.addEdge(entry.getKey(), entry.getValue());

I've left out a lot of error checking, simple constructors etc. but hopefully you get the idea.

Answer 2

Here I am assuming your parsing logic is correct and that's what you want. You need to initialize the hash2 within the first while loop and you really don't need temp1 at all.

int j=0;    
while ((str =in.readLine()) != null) {
            int foo = Integer.parseInt(str);
          HashMap<Integer, Integer> hash2=new HashMap<Integer, Integer>();
          while(foo>0){
                 remainder=foo % 10;
                   foo = foo / 10;
                 remainder2=foo%10;
                 foo=foo/10;
                 hash2.put(remainder2, remainder);
          }
          hash1.put(j, hash2);
          j++;
    }