title: How to merge short strings in a list into long strings
body: <p>Here I have a string list as follows:</p>
  <pre><code>List&lt;string&gt; str = new List&lt;string&gt; 
  { &quot;1&quot;, &quot;22&quot;, &quot;3&quot;, &quot;44&quot;, &quot;55&quot;, &quot;666666&quot;, &quot;7777777&quot;, &quot;8&quot;, &quot;99&quot; };
  </code></pre>
  <p>What I want is merging short strings into a long string of length less than n.</p>
  <p>Expect:</p>
  <pre><code>n = 5
  newlist = { &quot;1223&quot;, &quot;4455&quot;, &quot;666666&quot;, &quot;7777777&quot;, &quot;899&quot; };
  </code></pre>