Comments by saboor awan (Top 1 by date)

Actually this algo flood fill the bitmap in this manner. http://en.wikipedia.org/wiki/File:Smiley_fill.gif

so we have to check for that either on the right or left side, any area available to fill color or not.Therefore, we use spanleft and spanright checks.

obviously, there may be other methods to solve it. but is the most fastest algo known to me.