title: Find index for multiple elements in a long list
body: <p>I have a very long <code>lst</code> containing unique elements. I want to design a function which takes a list of elements as the input and it can return a list of index efficiently. We assume the items needed to find their index are all in the <code>lst</code>.</p>
  
  <p>Here is an example:</p>
  
  <pre><code>lst = ['ab','sd','ef','de']
  items_to_find = ['sd', 'ef', 'sd']
  &gt;&gt;&gt; fo(lst, items_to_find)  
  # Output: [1,2,1]
  </code></pre>
  
  <p>I have one solution of my own, but it looks less efficient.</p>
  
  <pre><code>&gt;&gt; [lst.index(x) for x in items_to_find]
  </code></pre>
  
  <p>Because the <code>lst</code> is very long, I need a very fast algorithm to solve it.</p>