Insert Delete GetRandom O(1)

Design a data structure that supports all following operations in O(1) time.

insert(val): Inserts an item val to the set if not already present.
remove(val): Removes an item val from the set if present.
getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

算法：使用set和vector搭配。set作爲主存器可以去重，vector作爲隨機數據發生器可以使用隨機下標。

class RandomizedSet {
public:
#define random(x) (rand()%x)
    set<int> docker;
    vector<int> nums;
    vector<int>::iterator lt;
    /** Initialize your data structure here. */
    RandomizedSet() {
        docker.clear();
    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    bool insert(int val) {
        if(docker.count(val))
            return false;
        else{
            docker.insert(val);
            nums.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(docker.count(val))   {
            docker.erase(val);
            lt = std::find(nums.begin(),nums.end(),val);
            nums.erase(lt);
            return true;
        }
        else
            return false;

    }
    /** Get a random element from the set. */
    int getRandom() {
        srand((unsigned int)time(0));
        int site = random(nums.size());
        return nums[site];
    }
};