class Grid(object):

	def __init__(self):

		self.cells = {}

		self.valuemap = {}

		self.minx = 0

		self.maxx = 0

		self.miny = 0

		self.maxy = 0

	def set(self, pos, value=1):

		if pos in self.cells and value != self.cells[pos]:

			self.clear(pos)

		if not pos in self.cells:

			self.cells[pos] = value

			if value in self.valuemap:

				self.valuemap[value].append(pos)

			else:

				self.valuemap[value] = [pos]

			self.update(pos)

		return self

	def clear(self, pos):

		if pos in self.cells: 

			self.valuemap[self.cells[pos]].remove(pos)

			del self.cells[pos]

			self.update(pos)

		return self

	def update(self, (x, y)):

		self.minx = min(x, self.minx)

		self.maxx = max(x, self.maxx)

		self.miny = min(y, self.miny)

		self.maxy = max(y, self.maxy)

		return self

	def width(self):

		return self.maxx - self.minx + 1

	def height(self):

		return self.maxy - self.miny + 1

	def __len__(self):

		return len(self.cells)

	def __str__(self):

		pass