insert-delete-getrandom-o1.py

# Time:  O(1)
# Space: O(n)

# Design a data structure that supports all following operations in O(1) time.
#
# insert(val): Inserts an item val to the set if not already present.
# remove(val): Removes an item val from the set if present.
# getRandom: Returns a random element from current set of elements.
# Each element must have the same probability of being returned.
#
# Example:
#
# // Init an empty set.
# RandomizedSet randomSet = new RandomizedSet();
#
# // Inserts 1 to the set. Returns true as 1 was inserted successfully.
# randomSet.insert(1);
#
# // Returns false as 2 does not exist in the set.
# randomSet.remove(2);
#
# // Inserts 2 to the set, returns true. Set now contains [1,2].
# randomSet.insert(2);
#
# // getRandom should return either 1 or 2 randomly.
# randomSet.getRandom();
#
# // Removes 1 from the set, returns true. Set now contains [2].
# randomSet.remove(1);
#
# // 2 was already in the set, so return false.
# randomSet.insert(2);
#
# // Since 1 is the only number in the set, getRandom always return 1.
# randomSet.getRandom();


from random import randint

class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.__set = []
        self.__used = {}
        

    def insert(self, val):
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.__used:
            return False

        self.__set += val,
        self.__used[val] = len(self.__set)-1

        return True
        

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.__used:
            return False

        self.__used[self.__set[-1]] = self.__used[val]
        self.__set[self.__used[val]], self.__set[-1] = self.__set[-1], self.__set[self.__used[val]]

        self.__used.pop(val)
        self.__set.pop()

        return True

    def getRandom(self):
        """
        Get a random element from the set.
        :rtype: int
        """
        return self.__set[randint(0, len(self.__set)-1)]


# Your RandomizedSet object will be instantiated and called as such:
# obj = RandomizedSet()
# param_1 = obj.insert(val)
# param_2 = obj.remove(val)
# param_3 = obj.getRandom()