380.InsertDeleteGetRandomO(1).py

"""
    Implement the RandomizedSet class:
    - bool insert(int val) Inserts an item val into the set if not present. 
      Returns true if the item was not present, false otherwise.
    - bool remove(int val) Removes an item val from the set if present. 
      Returns true if the item was present, false otherwise.
    - int getRandom() Returns a random element from the current set of elements 
      (it's guaranteed that at least one element exists when this method is 
      called). Each element must have the same probability of being returned.

    Follow up: Could you implement the functions of the class with each function 
    works in average O(1) time?

    Example:
    Input
    ["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
    [[], [1], [2], [2], [], [1], [2], []]
    Output
    [null, true, false, true, 2, true, false, 2]
    Explanation
                RandomizedSet randomizedSet = new RandomizedSet();
                randomizedSet.insert(1); // Inserts 1 to the set. Returns true 
                                         // as 1 was inserted successfully.
                randomizedSet.remove(2); // Returns false as 2 does not exist 
                                         // in the set.
                randomizedSet.insert(2); // Inserts 2 to the set, returns true. 
                                         // Set now contains [1,2].
                randomizedSet.getRandom(); // getRandom() should return either 
                                           // 1 or 2 randomly.
                randomizedSet.remove(1); // Removes 1 from the set, returns true.
                                         // Set now contains [2].
                randomizedSet.insert(2); // 2 was already in the set, so return 
                                         // false.
                randomizedSet.getRandom(); // Since 2 is the only number in the 
                                           // set, getRandom() will always 
                                           // return 2.

    Constraints:
        - -2**31 <= val <= 2**31 - 1
        - At most 105 calls will be made to insert, remove, and getRandom.
        - There will be at least one element in the data structure when 
          getRandom is called.
"""
#Difficulty: Medium
#18 / 18 test cases passed.
#Runtime: 556 ms
#Memory Usage: 17.9 MB

#Runtime: 556 ms, faster than 8.03% of Python3 online submissions for Insert Delete GetRandom O(1).
#Memory Usage: 17.9 MB, less than 62.45% of Python3 online submissions for Insert Delete GetRandom O(1).

import random

class RandomizedSet:

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

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

    def remove(self, val: int) -> bool:
        """
        Removes a value from the set. Returns true if the set contained the 
        specified element.
        """
        if val in self.set:
            self.set.remove(val)
            return True
        return False

    def getRandom(self) -> int:
        """
        Get a random element from the set.
        """
        return random.choice(self.set)


# 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()