For many languages in selector it doesn't provide any boilerplate code and cannot be solved by reading input since you don't know how binary tree composed. How can I use hakkerrank to prepare for interview

In some languages like Kotlin it gives only a main fucntion which doesn't have a Node class. And there's no explanation how the single array, that the input is giving, is sorted... I spent hours trying to figure out what the tree from the input should look like and I was trying to write a function to create the tree with Node class... So then I switched to Java and saw that the node object is given...

void solve(Node* root) { if(root == NULL) { return; } cout<data<<" "; solve(root->left); solve(root->right); }

solve(root);

Why it was showing main method in this?

My Java 8 solutions

Recursive approach

public static void preOrder(Node root) {
    if (root == null) return;

    System.out.print(root.data + " ");
    preOrder(root.left);
    preOrder(root.right);
}

Iterative approach

public static void preOrder(Node root) {
    if (root == null) return;

    Stack<Node> stack = new Stack<>();
    stack.push(root);

    while (!stack.isEmpty()) {
        Node current = stack.pop();
        System.out.print(current.data + " ");
				
        if (current.right != null) {
            stack.push(current.right);
        }

        if (current.left != null) {
            stack.push(current.left);
        }
    }
}