How to check if an integer is already in a list : <p>i'm currently coding my own Sudoku in Windows Forms C# and I currently have Problems how to check if an integer is already in my list.</p>

<pre><code>for (int i = 0; i &lt; 9; i++)
        {
            List&lt;int&gt; list = new List&lt;int&gt;();
            for(int j = 0; j &lt; 9; j++)
            {
                list.Add(sodukuPlayfield.grid[i, j]);
            }
        }
</code></pre>

<p>So I add all the number in a row to a list. But after that I wanna check if there is only one number from 1 - 9.
How can I solve this?</p>

<p>Thank you.</p>
