title: Comparing two strings finding first and last differences
body: <p>I have got two strings and i want to find the first and last differences.</p>
  
  <p><strong>I.E.:</strong></p>
  
  <p>S1: 'I helped a very nice old lady to cross the road.'</p>
  
  <p>S2: 'I helped an old lady to cross the road.'</p>
  
  <p><strong>Desired Output(check by words):</strong></p>
  
  <pre><code>[2,4] // 2 for 'a', 4 for 'nice'.
  </code></pre>
  
  <p>Because the differences are: 'I helped <code>a</code> <code>very</code> <code>nice</code> old lady to cross the road.'</p>
  
  <p><strong>Alternative Desired Output(check by chars):</strong></p>
  
  <pre><code>[10,21] // 10 for space, 20 for 'e'.
  </code></pre>
  
  <p>Because the difference is: 'I helped a<code>very nice</code> old lady to cross the road.'</p>
  
  <p>I can use any of them(or a third option), but the performance is an issue, because sometimes i perform this check dozens to hundreds times per sec.</p>