380.insert-delete-getrandom-o1.java

class RandomizedSet {
    HashMap<Integer, Integer> valueMap;
    HashMap<Integer, Integer> idxMap;
 
    /** Initialize your data structure here. */
    public RandomizedSet() {
        valueMap = new HashMap<>();
        idxMap = new HashMap<>();
    }
 
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    public boolean insert(int val) {
        if(valueMap.containsKey(val)){
            return false;
        }
 
        valueMap.put(val, valueMap.size());
        idxMap.put(idxMap.size(), val);
 
        return true;
    }
 
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    public boolean remove(int val) {
        if(valueMap.containsKey(val)){
            int idx = valueMap.get(val);
            valueMap.remove(val);
            idxMap.remove(idx);
 
            Integer tailElem = idxMap.get(idxMap.size());
            if(tailElem!=null){
                idxMap.put(idx,tailElem);
                valueMap.put(tailElem, idx);
            }
 
            return true;
        }
 
        return false;
    }
 
    /** Get a random element from the set. */
    public int getRandom() {
        if(valueMap.size()==0){
            return -1;
        }
 
        if(valueMap.size()==1){
            return idxMap.get(0);
        }
 
        Random r = new Random();
        int idx = r.nextInt(valueMap.size());
 
        return idxMap.get(idx);
    }
}