Design Phone Directory

这道题应该想到利用哈希表本身的无序随机性，我们可以生成各种不同的组合

class PhoneDirectory(object):

    def __init__(self, maxNumbers):
        """
        Initialize your data structure here
        @param maxNumbers - The maximum numbers that can be stored in the phone directory.
        :type maxNumbers: int
        """
        self.store = set([x for x in xrange(maxNumbers)])

    def get(self):
        """
        Provide a number which is not assigned to anyone.
        @return - Return an available number. Return -1 if none is available.
        :rtype: int
        """
        return self.store.pop() if self.store else -1

    def check(self, number):
        """
        Check if a number is available or not.
        :type number: int
        :rtype: bool
        """
        return number in self.store

    def release(self, number):
        """
        Recycle or release a number.
        :type number: int
        :rtype: void
        """
        self.store.add(number)


# Your PhoneDirectory object will be instantiated and called as such:
# obj = PhoneDirectory(maxNumbers)
# param_1 = obj.get()
# param_2 = obj.check(number)
# obj.release(number)