Leetcode - 380 o (1) time to insert, delete and get random elements (design hash table + array)

Hashtable +list

class RandomizedSet {
    
    // Put the value in list in   In order to random access 
    private List<Integer> list;
    //map Of key Is the value  map Of val yes   Values in list Position in 
    // For convenience in o(1) Within time   Insert delete value 
    private Map<Integer,Integer> map;
    public RandomizedSet() {
    
        list = new ArrayList<>();
        map = new HashMap<>();
    }
    
    public boolean insert(int val) {
    
          // If the value already exists 
          if(map.containsKey(val) == true)
            return false;
          else{
    
            // Newly added value index
            int index = list.size();
            // Added to the list
            list.add(val);
            // Added to the map
            map.put(val,index);
            return true;
          }
    }
    
    public boolean remove(int val) {
    
        //val non-existent   Delete failed 
        if(map.containsKey(val) == false)
           return false;
        else{
    
           //list The subscript of the last number 
         int lasti = list.size()-1;
         //list The value of the last number 
         int lastv = list.get(lasti);
         //val  stay list Subscript in 
         int vali = map.get(val);
         // take list The last number of is placed in val stay list Location 
         list.set(vali,lastv);
         // modify list The last number of is map Subscript in 
         map.put(lastv,vali);
         // Delete list The last number in 
         list.remove(lasti);
         // stay map Delete in val
         map.remove(val);
         return true;
        }
        
    }
    
    public int getRandom() {
    
        int n = list.size();
        // produce 0 - n-1 The random integer of the range 
        return list.get((int)(Math.random()*n));
    }
}

/** * 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(); */