【劍指offer】面試題21：包含min函數的棧

class StackWithMin:
	def __init__(self):
		self.data = []
		self.min_data = []
		self.size = 0

	def push(self, val):
		self.data.append(val)

		if len(self.min_data) == 0 or \
				self.min_data[-1] > val:
			self.min_data.append(val)

		else: 
			self.min_data.append(self.min_data[-1])
		self.size += 1


	def pop(self):
		if self.size > 0:
			del self.data[-1]
			del self.min_data[-1]
			self.size -= 1

	def min(self):
		return self.min_data[-1]