Sum of very very large numbers : <p>Given two very large numbers <code>a</code> and <code>b</code> where <code>a &lt; b</code>, the problem is to find the following sum:</p>

<pre><code>a + (a + 1) + (a + 2) + ... + (b - 2) + (b - 1) + b
</code></pre>

<p>The numbers <code>a</code> and <code>b</code> can be very very large (can contain millions of digits).</p>

<p>As these are very large numbers, programming languages cannot find the sum using integer data types. 
So, the only option is to use strings.</p>

<p>What is the most efficient way to do so?</p>
