title: Check if two Binary Search Tree have the same keys
body: <p>I am looking for a sequential algorithm (if exists) that tests if two BST have the same keys in <code>O(n)</code>, using <code>O(1)</code> memory and recursion is allowed.<br>
  How can you do: two <strong>synchronized</strong> in-order trasversal,so that it is possible to compare the <code>ith</code> element of both BST?</p>