title: Determine points within a given radius algorithm
body: <p>I'm not sure what mathematical concept this is to support my question. ^^</p>
  
  <p>Let's say we have PointA as the reference. The problem is to find the points around PointA within a given radius (Using coordinates). My approach would be to compute the distance of every point (Pythagorean) and then compare with the given radius. I'm sure that this would suck in terms of complexity.</p>
  
  <p>What algorithm may you suggest? 
  A sample code to point things out would be much appreciated. Thanks.</p>