Question

Below is my code:

class Node{
    int value;
    Node left;
    Node right;
    Node parent;
       //getters, setters
}

Create the Tree

    private static void createTree() throws FileNotFoundException{
    Map<String,Node> nodeMap = new HashMap<String,Node>();
    Scanner sc = new Scanner(new File("<location>"));
    int row =0;
    while(sc.hasNextLine()){
        String line = sc.nextLine();
        Scanner scanLine = new Scanner(line);
        System.out.println(line);
        int col =0;

        while(scanLine.hasNextInt()){
            int value = scanLine.nextInt();
            System.out.println(row+","+col+"="+value);
            Node node = new Node(value);
            nodeMap.put(row+","+col,node);
            if(row >0){
                if(col %2 ==0){
                    //left node
                    Node parent = nodeMap.get(row-1+","+col/2);
                    if(parent !=null){
                        node.setParent(parent);
                        parent.setLeft(node);
                    }
                }else{
                    //right node
                    Node parent = nodeMap.get(row-1+","+(col-1)/2);
                    if(parent !=null){
                        node.setParent(parent);
                        parent.setRight(node);
                    }
                }
            }
            col++;
        }
        row++;
    }
    System.out.println(nodeMap);
    Node root = nodeMap.get("0,0");
    traverseTree(root);
    System.out.println("sum="+sum);


}

Actual Traversal

    static int sum =0;
private static void traverseTree(Node n){
    if(n != null){
        sum+=n.value;
        traverseTree(n.left);
        traverseTree(n.right);
    }
}

I have 2 questions:

1. Read the input and create the tree: I read it from a file and store
   the root node in the hashmap. What are the alternatives?

2. In the recursive search, I am keeping the sum outside the function, so its possible to calculate the sum in a sequential fashion. Is it possible to keep the sum variable inside and return the total value at the end?

Answer 1

I read it from a file and store the root node in the hashmap. What are the alternatives?

How you are doing it seems pretty reasonable given the apparent input format, however I’d recommend using a List<List<Node>> rather than storing it with strings, as your performance may degrade fairly quickly because the strings are very similar, which may cause hash collisions, degrading your map’s performance greatly if the input is large.

In the recursive search, I am keeping the sum outside the function, so its possible to calculate the sum in a sequential fashion. Is it possible to keep the sum variable inside and return the total value at the end?

private static int traverseTree(Node n) {
    if (n != null) {
        return n.value + traverseTree(n.left) + traverseTree(n.right);
    } else {
        return 0;
    }
}