leetcode380

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(hash.count(val)) return false;
        hash[val] = vec.size();
        vec.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(hash.count(val)==0) return false;        
        int pos = hash[val];        
        hash[vec.back()] = pos;        
        swap(vec[pos], vec[vec.size()-1]);        
        hash.erase(val);        
        vec.pop_back();        
        return true;

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

private:
    unordered_map<int, int> hash;
    vector<int> vec;
};

/**
 * 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();
 */