title: Real-world example of exponential time complexity
body: <p>I'm looking for an intuitive, real-world example of a problem that takes (worst case) exponential time complexity to solve for a talk I am giving.</p>
  
  <p>Here are examples for other time complexities I have come up with (many of them taken from <a href="https://stackoverflow.com/questions/1592649/examples-of-algorithms-which-has-o1-on-log-n-and-olog-n-complexities">this SO question</a>):</p>
  
  <ul>
  <li>O(1) - determining if a number is odd or even</li>
  <li>O(log N) - finding a word in the dictionary (using binary search)</li>
  <li>O(N) - reading a book</li>
  <li>O(N log N) - sorting a deck of playing cards (using merge sort)</li>
  <li>O(N^2) - checking if you have everything on your shopping list in your trolley</li>
  <li>O(infinity) - tossing a coin until it lands on heads</li>
  </ul>
  
  <p>Any ideas?</p>