title: Is there an algorithm to determine contiguous colored regions in a grid?
body: <p>Given a basic grid (like a piece of graph paper), where each cell has been randomly filled in with one of n colors, is there a tried and true algorithm out there that can tell me what contiguous regions (groups of cells of the same color that are joined at the side) there are?  Let's say n is something reasonable, like 5.</p>
  
  <p>I have some ideas, but they all feel horribly inefficient.</p>