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I'm looking at the pseudocode on Wikipedia for this and trying to use it to write the algorithm in java. My question comes in a difference in how the result is returned. On wikipedia, one result is returned, and this breaks out of the search. In mine, everytime a relevant node is found, it is added to a list, and that list is to be returned when the tree has been processed. How would I detect the end of the tree in order to break out and return the list?

Wikipedia:

IDDFS(root, goal)
{
  depth = 0
  repeat
  {
    result = DLS(root, goal, depth)
    if (result is a solution)
      return result
    depth = depth + 1
  }
}

DLS(node, goal, depth) 
{
  if (depth == 0 and node == goal)
    return node
  else if (depth > 0)
    for each child in expand(node)
      DLS(child, goal, depth-1)
  else
    return null
}

Mine: 

    public List<String> dfid(Tree t, String goal)
    {
        List<String> results = new ArrayList<String>();
        String result;

        int depth = 0;
        while (true) //obviously not the way to go here
        {
            result = dls(t.root, goal, depth);
            if (result.contains(goal))
                results.add(result);
            depth += 1;
        }
        return results; //unreachable return
    }

    public String dls(Node node, String goal, int depth)
    {
        if (depth == 0 && node.data.contains(goal))
        {
            return node.data;
        }
        else if (depth > 0)
        {
            for(Node child : node.children)
            {
                dls(child, goal, depth-1);
            }
        }
        return null;
    }

Edit: After changes:

//depth first iterative deepening
        //control variables for these methods
        boolean maxDepth = false;
    List<String> results = new ArrayList<String>();

    public List<String> dfid(Tree t, String goal)
    {
        int depth = 0;

        while (!maxDepth)
        {
            maxDepth = true;
            dls(t.root, goal, depth);
            depth += 1;
        }
        return results;
    }

    public void dls(Node node, String goal, int depth)
    {
        if (depth == 0 && node.data.contains(goal))
        {
            //set maxDepth to false if the node has children
            maxDepth = maxDepth && children.isEmpty();
            results.add(node.data);
        }
        for(Node child : node.children)
        {
            dls(child, goal, depth-1);
        }
    }
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1 に答える 1

2

boolean maxDepth = falseインスタンス変数でこれを達成できると思います。while ループの各反復で、maxDepth == true終了する場合は、そうでなければ設定しmaxDepth = trueます。にdls到達したらdepth == 0を設定maxDepth = maxDepth && children.isEmpty()します。つまり、ノードに子がある場合は maxDepth を false に設定します。

また、dlsvoid メソッドに変更します。重複を除外するかどうかに応じてreturn node.data、またはにresults.add(node.data)置き換えます。resultsArrayListHashSet

ツリー内のすべてのノードに常にアクセスする場合は、次のように変更dlsします。

public void dls(ArrayList<String> results, Node node, String goal)
{
    if (node.data.contains(goal))
    {
        results.add(node.data);
    }
    for(Node child : node.children)
    {
        dls(child, goal, depth-1);
    }
}
于 2013-04-15T00:46:20.080 に答える