My solution in C++

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

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?