title: How to calculate the upper bound time complexity (`"big O`") of a recursive function?
body: <p>Suppose I have a recursive function <code>T</code>, and I want to calculate the upper bound timer complexity of this function.</p>
  
  <p>T(1) = 3</p>
  
  <p>T(n) = 3T(n/3) + 3.</p>
  
  <p>How can I find the upper bound of the time complexity of T(n)?</p>