PU Insert Delete GetRandom O(1)

// 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 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

class RandomizedSet(object):

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

    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.d: return False
        self.l.append(val)
        self.d[val] = len(self.l) - 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.d: return False
        ind = self.d[val]
        self.l[ind] = self.l[-1]
        self.d[self.l[ind]] = ind
        del self.d[val]
        self.l.pop()
        return True


    def getRandom(self):
        """
        Get a random element from the set.
        :rtype: int
        """
        if not self.l: return -1
        return random.choice(self.l)


# 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()