380. 常数时间插入、删除和获取随机元素/C++

class RandomizedSet {
    unordered_map<int,int> hash;
    vector<int> vec;
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(hash.count(val))
            return false;
        vec.push_back(val);
        hash[val] = vec.size()-1;
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if(!hash.count(val))
            return false;
        hash[vec.back()] = hash[val];
        swap(vec.back(),vec[hash[val]]);
        vec.pop_back();
        hash.erase(val);
        return true;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        if(vec.empty()) return 0;
        return vec[rand()%vec.size()];
    }
};

/**
 * 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();
 */