Solved

Problem using recursive function to compare trees in Java

Posted on 2012-04-09
5
540 Views
Last Modified: 2012-04-15
Hi

I have to find the best matching subtrees in two xml trees.
here is the code (in brief):

public static void FindBestMatchingSubtree(int doc1, int doc2, Node n1, Node n2, SQLScript statement) {
        // retrieve internal nodes for the first and second trees  
        
        ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc1, n1);
        ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc2, n2);

        for (Node t1childNode : t1Nodes) {  // to iterate child nodes of the 1st ArrayList
            for (Node t2childNode : t2Nodes) {  // to iterate child nodes of the 2nd ArrayList
                
                if (t1childNode.getNodeName().equals(t2childNode.getNodeName())) {
                    score = calculateScore(t1childNode, t2childNode, statement);
                    
                    // Test if two pair of nodes for the two trees are matched
                    if (score == 1.0) { // Identical nodes
                        System.out.println("Identical");
                    }
                    else if ((score < 1.0) && (score > 0)) { // Matched nodes (semi)
                        System.out.println("Matched");
                        // recursively match the child nodes of the current ones 
                        FindBestMatchingSubtree(doc1, doc2, t1childNode, t2childNode, statement);    
                    }
                } // end if

            }  // end for
            // Just hint for the output
            System.out.println("Finish one child from the first tree");
        }  // end for
    }

Open in new window


Job of the function:
- It takes as input two document ids and two nodes of them (say root nodes of XML document.
- It then create two ArrayLists of child nodes for both given nodes n1 & n2.
- It will then compare pairs of nodes to find if they are Identical or matched (using special function calculateScore).
- If they are identical, print that.
- If they are matched (not exactly the same), go deeper and repeat the process by comparing child nodes of the current pair.

The problem:
I get wrong result because I think when the function (FindBestMatchingSubtree) is called inside itself it will repeat creating the two ArrayLists: t1Nodes & t2Nodes, which is wrong

Can anyone help to achieve the goal without having such a problem

Regards
0
Comment
Question by:hamsalgla
  • 2
  • 2
5 Comments
 
LVL 11

Assisted Solution

by:anilallewar
anilallewar earned 100 total points
ID: 37826686
The array lists t1Nodes & t2Nodes that are created with each recursive call is fine as those would be different objects that get created on stack.

What is the significance of int doc1, int doc2 as they get passed for each recursive call but don't change within the execution?

I will need more information including the code to make further suggestions.
0
 
LVL 20

Expert Comment

by:gatorvip
ID: 37827270
>>I get wrong result

How can you tell? Please post sample data, the resulting output using your code and the desired output
0
 
LVL 20

Assisted Solution

by:gatorvip
gatorvip earned 100 total points
ID: 37827279
>>       ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc1, n1);
        ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc2, n2);

Check your code, this should probably say t2Nodes. I assume this is just a copy/paste typo in here as in real code you should be getting an error (t2Nodes would be undefined).
0
 

Accepted Solution

by:
hamsalgla earned 0 total points
ID: 37828202
What is the significance of int doc1, int doc2 as they get passed for each recursive call but don't change within the execution?

doc1 and doc2 are passed as parameters getInternalChildNodes function to get the list of nodes for doc1 and doc1 (see line 4 and 5).
They do not affect the results.

>>       ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc1, n1);
        ArrayList<Node> t1Nodes = statement.getInternalChildNodes(doc2, n2);

Check your code, this should probably say t2Nodes. I assume this is just a copy/paste typo in here as in real code you should be getting an error (t2Nodes would be undefined).

Yes I made a typo mistake.

Actually I found the problem. that is a exit from the function:
if (t1Nodes.isEmpty() || t2Nodes.isEmpty()) {
            System.exit(0);
}

Open in new window

It was in line 9 (inside the two loops)
I remove it from the code here because I thought it is not significant.
When I replace it with If..Else condition, the program works fine and I get the correct results.

Thanks guys for your helps.

I will back to you as soon as i have probs since this is just a very small part of my big project :)

Regadrs
0
 

Author Closing Comment

by:hamsalgla
ID: 37848065
Calling 'System.exit()' inside the function can be a good practice as long as you know it will not end the program unexpectedly.

Use 'if, else' statement instead.
0

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

One of Google's most recent algorithm changes affecting local searches is entitled "The Pigeon Update." This update has dramatically enhanced search inquires for the keyword "Yelp." Google searches with the word "Yelp" included will now yield Yelp a…
Article by: Nadia
Linear search (searching each index in an array one by one) works almost everywhere but it is not optimal in many cases. Let's assume, we have a book which has 42949672960 pages. We also have a table of contents. Now we want to read the content on p…
Viewers will learn about arithmetic and Boolean expressions in Java and the logical operators used to create Boolean expressions. We will cover the symbols used for arithmetic expressions and define each logical operator and how to use them in Boole…
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…

708 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now