CareerCup

1. Use Java Serialization on the tree & tree nodes and then deserialize this tree.
2. Write the pre/post traversal of the trees to the disk as text and recreate the tree.

package algos;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Queue;

/**
 * Created by paramasivami on 4/10/16.
 */
public class SerializeTree {

    //Tree Node.
    public static class Node{
        private int data;
        //Set of children.
        private List<Node> children;

        public Node(){
            this.children = new ArrayList<>();
        }
        public Node(int data){
            this.data = data;
            this.children = new ArrayList<>();
        }

        public int getData() {
            return data;
        }

        public void setData(int data) {
            this.data = data;
        }

        public List<Node> getChildren() {
            return children;
        }

        public void setChildren(List<Node> children) {
            this.children = children;
        }

        public void addChildrenNode(Node child){
            this.children.add(child);
        }
    }

    public static StringBuffer traversal(StringBuffer s, Node root){

        if(root.getChildren().size() == 0) {
            s.append(String.valueOf(root.data)).append(",");
            s.append("#").append(",");
        }
        else{
            s.append(String.valueOf(root.data)).append(",");
            root.children.forEach(
                    child -> traversal(s, child)
            );
        }


        return s;
    }

    public static Node constructTree(Queue queue, Node result){

            String s = (String) queue.remove();
            if(!s.equals("#")){
                result = new Node(Integer.parseInt(s));
                Node n = constructTree(queue, result);
                if(n != null)
                    result.addChildrenNode(n);
                else
                    return result;
            }
            else{
                return null;
            }
        return result;
    }

    public static void main(String[] args) {


        //construct tree.
        Node s = new Node(1);
        Node s1 = new Node(2);
        Node s2 = new Node(3);
        Node s3 = new Node(4);
        Node s4 = new Node(5);
        s1.setChildren(Arrays.asList(s4));

        s.setChildren(Arrays.asList(s1,s2,s3));
        StringBuffer result = traversal(new StringBuffer(),s);
        Queue<String> queue = new ArrayDeque<>();
        queue.addAll(Arrays.asList(result.toString().split(",")));

        //Serialize it.
        queue.forEach(System.out::print);

        System.out.println();
        Node node = new Node();
        Node firstNode = new Node();
        int count = 0;

        //De Serialize it
        while(!queue.isEmpty()){

            if(count == 0){
                firstNode = constructTree(queue, node);
                count++;
            }
            else{
                firstNode.addChildrenNode(constructTree(queue, node));
            }

        }

        //Traverse the deserialized node. so that we can see the result and check whether it is true or not.
        System.out.println(traversal(new StringBuffer(), firstNode));
    }

}