PreorderTraversal.java

package Tree;


import java.util.ArrayList;
import java.util.Stack;

public class Node {
    int data;
    Node left, right;
    Node(int data){
        this.data = data;
        left = null;
        right = null;

    }

}
/*class Binary1{
    static void inOrderTrav(Node curr, ArrayList < Integer > inOrder){
        if (curr == null){
            return;
        }
        inOrderTrav(curr.left, inOrder);
        inOrder.add(curr.data);
        inOrderTrav(curr.right, inOrder);
    }
}*/
class Binary1 {
    static ArrayList< Integer > preOrderTrav(Node curr){
        ArrayList <Integer> preOrder = new ArrayList <Integer>();
        if (curr == null)
            return preOrder;
        Stack <Node> s = new Stack <>();
        s.push(curr);

        while(!s.isEmpty()){
            Node topNode = s.peek();
            preOrder.add(topNode.data);
            s.pop();
            if(topNode.right != null)
                s.push(topNode.right);
            if(topNode.left != null)
                s.push(topNode.left);

        }
        return preOrder;
    }

    public static void main(String args[]){

        Node root = new Node(1);
        root.left = new Node(2);
        root.right = new Node(3);
        root.left.left = new Node(4);
        root.left.right = new Node(5);
        root.left.right.left = new Node(8);
        root.right.left = new Node(6);
        root.right.right = new Node(7);
        root.right.right.left = new Node(9);
        root.right.right.right= new Node(10);

        ArrayList<Integer> preOrder;
        preOrder = preOrderTrav(root);

        System.out.println("The preOrder Traversal is : ");
        for(int i = 0; i < preOrder.size(); i++){
            System.out.print(preOrder.get(i) + " ");
        }
    }
}