380. Insert Delete GetRandom O(1)

class RandomizedSet {
public:
    /** Initialize your data structure here. */
    RandomizedSet() {

    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    bool insert(int val) {
        if (idx.count(val)) return false;
        idx[val] = nums.size();
        nums.push_back(val);
        return true;
    }

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if (!idx.count(val)) return false;
        nums[idx[val]] = nums.back();
        idx[nums.back()] = idx[val];
        idx.erase(val);
        nums.pop_back();
        return true;
    }

    /** Get a random element from the set. */
    int getRandom() {
        return nums[rand() % nums.size()];
    }

private:
    vector<int>nums;
    unordered_map<int, int> idx;
};

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * RandomizedSet obj = new RandomizedSet();
 * bool param_1 = obj.insert(val);
 * bool param_2 = obj.remove(val);
 * int param_3 = obj.getRandom();
 */