LeetCode: Design Phone Directory

Posted on February 12, 2018July 26, 2020 by braindenny

Design Phone Directory

Similar Problems:

Design a Phone Directory which supports the following operations:

get: Provide a number which is not assigned to anyone.
check: Check if a number is available or not.
release: Recycle or release a number.

Example:

// Init a phone directory containing a total of 3 numbers: 0, 1, and 2.
PhoneDirectory directory = new PhoneDirectory(3);

// It can return any available phone number. Here we assume it returns 0.
directory.get();

// Assume it returns 1.
directory.get();

// The number 2 is available, so return true.
directory.check(2);

// It returns 2, the only number that is left.
directory.get();

// The number 2 is no longer available, so return false.
directory.check(2);

// Release number 2 back to the pool.
directory.release(2);

// Number 2 is available again, return true.
directory.check(2);

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## https://code.dennyzhang.com/design-phone-directory
## Basic Ideas: One collection: free_set
##
##  Notcie: here we only need one collection(free_set), instead of two (occupied_set and free_set)
## Complexity: Time O(1), Space O(n)
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.free_set = set(range(0, 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.free_set.pop() if len(self.free_set) != 0 else -1

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

    def release(self, number):
        """
        Recycle or release a number.
        :type number: int
        :rtype: void
        """
        if number not in self.free_set: self.free_set.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)

Post Views: 5