title: Retrieve unique characters from 2 strings
body: <p>I would like to retrieve &quot;ed&quot; from these strings (&quot;abce&quot;, &quot;abcd&quot;) because they are unique letters when compared to each other. How can I fix my codes? Thanks.</p>
  <pre><code>def solve(a,b):
      box = []
      for i in a:
          for j in b:
              if i != j and i not in box:
                  box.append(i)
      return ''.join(box)
  
  print(solve(&quot;abce&quot;,&quot;abcd&quot;)) &lt; ----- Answer : abce
  </code></pre>