title: merge two sorted arrays in-place in ascending order
body: <p>merge two sorted arrays in-place in ascending order.
  Eg:</p>
  
  <pre><code>A[]=7,15,21
  B[]=5,12
  </code></pre>
  
  <p>Output</p>
  
  <pre><code>A[]=5,7,12
  B[]=15,21
  </code></pre>
  
  <p>You can't take any extra memory space except few variables.</p>