def floodFill(x:Int, y:Int, c:Char) = {
                    def fill(s:Set[(Int, Int)], c:Char, t:Char):Unit = {
                            val (x,y) = s.head
                            val current_color = colorAt(x,y)
                            if(current_color == t && current_color != c) {
                                    plotPixel(x, y, c)
                                    val left = if(x > 0) Set((x-1,y)) else Set()
                                    val right = if(x < width-1) Set((x+1,y)) else Set()
                                    val up = if(y > 0) Set((x,y-1)) else Set()
                                    val down = if(y < height-1) Set((x,y+1)) else Set()
                                    fill(s.tail ++ left ++ right ++ up ++ down, c, t)
                            } else if(!s.tail.isEmpty) {
                                    fill(s.tail, c, t)
                            }
                    }
     
                    val source_color = colorAt(x,y)
                    val s = Set((x,y))
                    fill(s, c, source_color)
            }