380 O(1) 时间插入、删除和获取随机元素

https://leetcode.cn/leetbook/read/top-interview-questions-medium/xw5rt1/

cost: 15m58s

class RandomizedSet {
public:
    RandomizedSet() {
        std::random_device rd;
        this->gen = std::mt19937(rd());
    }

    bool insert(int val) {
        if (m.count(val)) {
            return false;
        }
        vec.push_back(val);
        m[val] = vec.size() - 1;
        return true;
    }

    bool remove(int val) {
        if (!m.count(val)) {
            return false;
        }
        int idx = m[val];
        std::swap(vec[idx], vec[vec.size() - 1]);
        m[vec[idx]] = idx;
        vec.pop_back();
        m.erase(val);
        return true;
    }

    int getRandom() {
        std::uniform_int_distribution<> dis(0, vec.size() - 1);
        int idx = dis(this->gen);
        return vec[idx];
    }

private:
    unordered_map<int, int> m;
    vector<int> vec;
    std::mt19937 gen;
};

/**
 * 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();
 */