380. Insert Delete GetRandom O(1)

class RandomizedSet {
    Map<Integer, Integer> m;
    List<Integer> l;
    Random rand = new Random();

    /** Initialize your data structure here. */
    public RandomizedSet() {
        m = new HashMap<Integer, Integer>();
        l = 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 (m.containsKey(val)) return false;
        
        m.put(val, l.size());
        l.add(l.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 (! m.containsKey(val)) return false;
        
        int loc = m.get(val);
        int last = l.get(l.size() - 1);
        l.set(loc, last);
        m.put(last, loc);
        l.remove(l.size()-1);
        m.remove(val);
        return true;
    }
    
    /** Get a random element from the set. */
    public int getRandom() {
        return l.get(rand.nextInt(l.size()));
    }
}

/**
 * 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();
 */

Runtime: 7 ms, faster than 99.93% of Java online submissions for Insert Delete GetRandom O(1).
Memory Usage: 43.8 MB, less than 73.72% of Java online submissions for Insert Delete GetRandom O(1).

이거...자신감이 넘처오르네요 ㅎ