leetcode 381. Insert Delete GetRandom O(1) - Duplicates allowed

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Design a data structure that supports all following operations in average O(1) time.

Note: Duplicate elements are allowed.

  1. insert(val): Inserts an item val to the collection.
  2. remove(val): Removes an item val from the collection if present.
  3. getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.

Example:


// Init an empty collection.
RandomizedCollection collection = new RandomizedCollection();

// Inserts 1 to the collection. Returns true as the collection did not contain 1.
collection.insert(1);

// Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1].
collection.insert(1);

// Inserts 2 to the collection, returns true. Collection now contains [1,1,2].
collection.insert(2);

// getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.
collection.getRandom();

// Removes 1 from the collection, returns true. Collection now contains [1,2].
collection.remove(1);

// getRandom should return 1 and 2 both equally likely.
collection.getRandom();

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import collections
class RandomizedCollection:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums = []
        self.dic = collections.defaultdict(set)

    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
        """
        self.nums.append(val)
        self.dic[val].add(len(self.nums) - 1)
        return len(self.dic[val]) == 1

    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.dic[val]:
            rmindex,lastval = self.dic[val].pop(),self.nums[-1]
            self.nums[rmindex] = lastval
            self.dic[lastval].add(rmindex)
            self.dic[lastval].discard(len(self.nums)-1)
            self.nums.pop()
            return True
        return False
        

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


# 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()