title: How to find or count the duplicate in multidimensional array in c#
body: <p>I am creating a <strong>2d</strong> <code>(3 * 3)</code> array in c# which has to count or find the <em>duplicate</em> value</p>
  
  <pre><code>int[,] arr = new int[3, 3] {
     {1, 2, 6},
     {4, 1, 5},
     {6, 1, 8}
  };
  </code></pre>
  
  <p>I expected the output has <code>1</code> and <code>6</code> are the <em>duplicate values</em></p>
  
  <p>For beginners only with <code>for</code> loop</p>