text: //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();
  
  class RandomizedSet {
      HashMap<Integer, Integer> map;
      ArrayList<Integer> values;
  
      /** Initialize your data structure here. */
      public RandomizedSet() {
          map = new HashMap<Integer, Integer>();
          values = new ArrayList<Integer>();
      }
      
      /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
      public boolean insert(int val) {
          if(!map.containsKey(val)) {
              map.put(val, val);
              values.add(val);
              return true;
          }
          else {
              return false;
          }
      }
      
      /** Removes a value from the set. Returns true if the set contained the specified element. */
      public boolean remove(int val) {
          if(map.containsKey(val)) {
              map.remove(val);
              values.remove(values.indexOf(val));
              return true;
          }
          return false;
      }
      
      /** Get a random element from the set. */
      public int getRandom() {
          int random = (int)(Math.random() * values.size());
          int valueToReturn = values.get(random);
          return map.get(valueToReturn);
      }
  }
  
  /**
   * Your RandomizedSet object will be instantiated and called as such:
   * RandomizedSet obj = new RandomizedSet();
   * boolean param_1 = obj.insert(val);
   * boolean param_2 = obj.remove(val);
   * int param_3 = obj.getRandom();
   */
  