Insert Delete GetRandom O(1) - Duplicates allowed

Problem: Insert Delete GetRandom O(1) - Duplicates allowed

Code in Python:

from collections import defaultdict

class RandomizedCollection(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.m = defaultdict(set)
        self.l = []
        self.i = 0


    def insert(self, val):
        """
        Inserts a value to the collection. Returns true if the collection did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        res = False
        if not self.m[val]: res = True

        self.m[val].add(self.i)
        self.l.append(val)
        self.i += 1

        return res


    def remove(self, val):
        """
        Removes a value from the collection. Returns true if the collection contained the specified element.
        :type val: int
        :rtype: bool
        """
        if self.m[val]:
            index = self.m[val].pop()
            last = self.l[-1]
            self.m[last].add(index)
            self.m[last].discard(self.i-1)
            self.l[index], self.l[-1] = self.l[-1], self.l[index]
            self.l.pop()
            self.i -= 1
            return True
        return False


    def getRandom(self):
        """
        Get a random element from the collection.
        :rtype: int
        """
        return random.choice(self.l)



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