380. Insert Delete GetRandom O(1).cpp

// 92ms, O(n) getRandom()
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(s.count(val)) return false;
        s.insert(val);
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if(!s.count(val)) return false;
        s.erase(val);
        return true;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        auto p = s.begin();
        advance(p, rand() % s.size());
        return *p;
    }

private:
    unordered_set<int>s;
};

/**
 * 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();
 */

// 48ms, 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(m.count(val)) return false;
        m[val] = v.size();
        v.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(!m.count(val)) return false;
        int num = v.back();
        m[num] = m[val];
        v[m[val]] = num;
        v.pop_back();
        m.erase(val);
        return true;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        return v[rand() % v.size()];
    }

private:
    unordered_map<int, int>m;
    vector<int>v;
};

/**
 * 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();
 */