title: find element in list 1 that is in list 2
body: <p>I have written the following code to find elements in a list that are also within another list. However This algorithm is n squared in Big O, is there a better way of getting around this?
  thanks in advance</p>
  
  <pre><code>def printCommon(list1,list2):
      for i in list1:
          found = False
          for j in list2:
              if i == j:
                  print i
                  break
  if __name__ == "__main__":
      list1 = [1,2,3,4,5]
      list2 = [9,8,7,6,5]
      printCommon(list1,list2)
  </code></pre>