findMin()

/* Find the minimum key of the BST */
public Key findMin() {
   return findMin(root).key;                                    // 1
}

/* Private findMin() method */
private Node<Key, Value> findMin(Node<Key, Value> x) {
   if (x.left == null) {                                        // 2
       return x;                                                // 2
   }
   return findMin(x.left);                                      // 3
}