Given a binary tree, write a method to recursively traverse the tree in the preorder manner. Mark a node as visited by adding its data to the list - Arraylist <Integer> preorderedList.
Pre-order traversal
1. Add the data of the current node to the Arraylist.
2. Traverse the left subtree by recursively calling the preorder method.
3. Traverse the right subtree by recursively calling the preorder method.
//Populated the elements of the tree in the below list in preorder format
ArrayList<Integer> preorderedList = new ArrayList<Integer>();
public void preorder(TreeNode root) {
}
