old_contents: # Time:  O(1)
  # Space: O(1)
  
  # 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()
  
new_contents: # 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()
  
subject: Update insert-delete-getrandom-o1.py