Most memory efficient way to merge two files
<p>I need to merge two files while also applying a sort. It is important the I keep the task light on memory usage. I need to create a console app in c# for this.</p>

<p>Input File 1:</p>

<blockquote>
  <p><em>Some Header</em><br>
  A12345334<br>
  A00123445<br>
  A44566555<br>
  B55677<br>
  B55683<br>
  B66489<br>
  <em>record count: 6</em></p>
</blockquote>

<p>Input File 2:</p>

<blockquote>
  <p><em>Some Header</em><br>
  A00123465<br>
  B99423445<br>
  <em>record count: 2</em></p>
</blockquote>

<p>So, I need to make sure that the third file should have all the "A" records coming first and then the "B" records followed by the Total record count.</p>

<p>Output File:</p>

<blockquote>
  <p><em>Some header</em><br>
  A12345334<br>
  A00123445<br>
  A44566555<br>
  A00123465<br>
  B99423445<br>
  B55677<br>
  B55683<br>
  B66489<br>
  <em>record count: 8</em></p>
</blockquote>

<p>Record sorting within "A" and "B" is not relevant.</p>
