Insert, Delete, getRandom in O(1) Time

Write a C# program to design a data structure that supports the following operations in O(1) time: 1. Insert(val): Inserts an item val into the set if not already present. 2. Remove(val): Removes an item val from the set if present. 3. GetRandom(): Returns a random element from the current set of elements. Each element must have the same probability of being returned.

Example 1

  
Input: 
["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]

[[], [1], [2], [2], [], [1], [2], []]
  
Output: [null, true, false, true, 2, true, true, 2]
  
Explanation: 
    

      
RandomizedSet randomizedSet = new RandomizedSet();
      
randomizedSet.insert(1);    // Returns true because 1 was inserted successfully
      
randomizedSet.remove(2);    // Returns false because 2 does not exist in the set
      
randomizedSet.insert(2);    // Returns true because 2 was inserted successfully
      
randomizedSet.getRandom();  // Returns 2 (randomly chosen from [1, 2])
      
randomizedSet.remove(1);    // Returns true because 1 was removed successfully
      
randomizedSet.insert(2);    // Returns false because 2 already exists in the set
      
randomizedSet.getRandom();  // Returns 2 (the only number in the set)
    
  

Example 2

  
Input: 
["RandomizedSet", "insert", "insert", "remove", "insert", "remove", "getRandom"]

[[], [1], [2], [1], [3], [3], []]
  
Output: [null, true, true, true, true, true, 2]
  
Explanation: 
    

      
RandomizedSet randomizedSet = new RandomizedSet();
      
randomizedSet.insert(1);    // Returns true because 1 was inserted successfully
      
randomizedSet.insert(2);    // Returns true because 2 was inserted successfully
      
randomizedSet.remove(1);    // Returns true because 1 was removed successfully
      
randomizedSet.insert(3);    // Returns true because 3 was inserted successfully
      
randomizedSet.remove(3);    // Returns true because 3 was removed successfully
      
randomizedSet.getRandom();  // Returns 2 (the only number left in the set)
    
  

Constraints

  
-2^31 ≤ val ≤ 2^31 - 1
  
At most 2 * 10^5 calls will be made to insert, remove, and getRandom
  
There will be at least one element in the data structure when getRandom is called
  
Time Complexity: O(1) for all operations
  
Space Complexity: O(n) where n is the number of elements stored