title: Time complexity - understanding big-Theta
body: <p>I'm currently taking algorithms and data structure. After nearly two months of studying, I still find time complexity extremely confusing.</p>
  
  <p>I was told (by my professor) that if I big-omega and big-O of some program aren't equal, big-theta doesn't exist.</p>
  
  <p>I now literally question everything I've learned so far. I'll take BubbleSort as an example, with big-omega(n),big-theta(n^2) and big-O(n^2). Big-theta indeed does exist (and it makes sense when i analyze it).</p>
  
  <p>Can anyone explain to me whether my professor is wrong or perhaps I misunderstood something?</p>