Design a data structure that supports all following operations in average 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 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

Difficulty: interview

Starter code:

class RandomizedSet:
    def __init__(self):
        """
        Initialize your data structure here.
        """
    def insert(self, val: int) -> bool:
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        """
    def remove(self, val: int) -> bool:
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        """
    def getRandom(self) -> int:
        """
        Get a random element from the 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()

Solutions:
import random
         
 class RandomizedSet:
 
     def __init__(self):
         """
         Initialize your data structure here.
         """
         self.dict = {}
         self.list = []
         
 
     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.dict:
             return False
         self.dict[val] = len(self.list)
         self.list.append(val)
         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.dict:
             return False
         self.list[self.dict[val]] = self.list[-1]
         self.dict[self.list[-1]] = self.dict[val]
         self.list.pop()
         self.dict.pop(val)
         return True
 
     def getRandom(self):
         """
         Get a random element from the set.
         :rtype: int
         """
         return random.choice(self.list)
 
 
 # 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()

import random
 class RandomizedSet:
 
     def __init__(self):
         """
         Initialize your data structure here.
         """
         self.dataMap = {}
         self.dataList = []
         
 
     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.dataMap:
             return False
         else:
             self.dataMap[val] = len(self.dataList)
             self.dataList.append(val)
             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 in self.dataMap:
             idx = self.dataMap[val]
             tail = self.dataList.pop()
             if idx < len(self.dataList):
                 self.dataList[idx] = tail
                 self.dataMap[tail] = idx
             del self.dataMap[val]
             return True
         else:
             return False
 
         
         
 
     def getRandom(self):
         """
         Get a random element from the set.
         :rtype: int
         """
         return random.choice(self.dataList)
         
 
 
 # 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()

class RandomizedSet:
 
     def __init__(self):
         """
         Initialize your data structure here.
         """
         self.dic = {}
         self.l = []
 
     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.dic:
             return False
         self.l.append(val)
         self.dic[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.dic:
             return False
         self.dic[self.l[-1]] = self.dic[val]
         self.l[self.dic[val]], self.l[-1] = self.l[-1], self.l[self.dic[val]]
         self.l.pop()
         del self.dic[val]
         return True
 
     def getRandom(self):
         """
         Get a random element from the set.
         :rtype: int
         """
         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()