Node* build(Node* root, int level, int l){
    if(l < level && !root){
        root = new Node(1);
        root->left = build(root->left, level, l + 1);
        root->right= build(root->right, level, l + 1);
    }
    return root;
}
void printBinary(Node* root, std::string str){
    if(root){
        printBinary(root->left, str + "0");

        if(root->left == NULL && root->right == NULL)
            std::cout<<"["<<str<<"]"<<std::endl;
        
        printBinary(root->right, str + "1");
    }
}