void decode_huff(node * root, string s) 
{
    string result = "";
    node * currNode = root;
    auto it = s.begin();
    
    while (it != s.end())
    {
        // Read s and traverse until we reach a leaf.
        while (currNode->data == '\0')
        {
            if (*it == '0')
            {
                currNode = currNode->left;
            }
            else if (*it == '1')
            {
                currNode = currNode->right;
            }
            else 
            {
                cout << "Error";
            }
            
            it++;
        }
        
        // Leaf. Get letter and reset.
        result += currNode->data;
        currNode = root;
    }
    
    cout << result;
}