12-InsertDeleteGetRandom.cpp

class RandomizedSet {
public:
    /** Initialize your data structure here. */
    unordered_map<int, int> s;
    vector<int> v;
    RandomizedSet() {
        srand(time(NULL));
    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    bool insert(int val) {
        if (s.find(val) != s.end()) return false;
        v.push_back(val);
        s[val] = v.size() - 1;
        return true;
    }

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if (s.find(val) == s.end()) return false;
        s[v[v.size() - 1]] = s[val];
        v[s[val]] = v[v.size() - 1];
        v.pop_back();
        s.erase(val);
        return true;
    }

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