Insert Delete Get Random

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 map; ArrayList 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);
}

}

Insert Delete Get Random Solution