title: How to delete duplicates in dictionary with list values
body: <p>I need to delete the elements that are duplicated in a dictionary like this:</p>
  <pre><code>{
      1: ['1', '2', '3'],
      2: ['4', '3', '6', '7'],
      3: ['8', '1', '9']
  }
  </code></pre>
  <p>as to make the final result like this</p>
  <pre><code>{
      1: ['1', '2', '3'],
      2: ['4', '6', '7'],
      3: ['8', '9']
  }
  </code></pre>
  <p>Please help me how to do that, I have no idea</p>