380. Insert Delete GetRandom O(1)

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本文介绍了一种在平均O(1)时间内支持插入、删除和随机获取元素的随机集合数据结构设计。通过结合使用map和vector，实现了高效的操作，解决了传统set在随机获取元素时的效率问题。

Design a data structure that supports all following operations in average 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.

Example:

// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();

// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);

// Returns false as 2 does not exist in the set.
randomSet.remove(2);

// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);

// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();

// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);

// 2 was already in the set, so return false.
randomSet.insert(2);

// Since 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

最开始自己给出的方案是用 set 来实现不借助任何别的数据结构和变量，仅用一个set，涉及到了set的读取，count函数等，

但在实现获取随机数时出现问题，不能正常获得。

参考网上大部分的实现是借助于map和unordered_map来实现，我的版本后来基于map来实现，对map比较熟悉一点。

/*class RandomizedSet {
    //RandomizedSet randomSet = new RandomizedSet();
    std::set<int> dataArray;
public:
    /** Initialize your data structure here. */
/*    RandomizedSet() {
        //std::set<int> dataArray;
        dataArray.clear();
    }*/

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
/*    bool insert(int val) {
        std::set<int>::iterator it=dataArray.find(val);
        if(it==dataArray.end()){
            dataArray.insert(val);
            return true;
        }
        else{
            return false;
        }

    }*/

    /** Removes a value from the set. Returns true if the set contained the specified element. */
/*    bool remove(int val) {
        std::set<int>::iterator it=dataArray.find(val);
        if(it==dataArray.end()){
            //dataArray.erase(val);
            return false;
        }
        else{
            dataArray.erase(val);
            return true;
        }

    }*/

    /** Get a random element from the set. */
/*    int getRandom() {
        int size = dataArray.size();
        cout<<"size:"<<size<<endl;
        int loc = rand()%size;
        std::cout<<"loc is:"<<loc<<std::endl;
        return dataArray.count(loc);
    }
};*/

class RandomizedSet {
private:
    std::map<int,int> dataMap;
    std::vector <int> dataVec;
    //RandomizedSet randomSet = new RandomizedSet();
    // std::set<int> dataArray;
public:
    /** Initialize your data structure here. */
    RandomizedSet() {
        //std::set<int> dataArray;
        // dataArray.clear();
        dataMap.clear();
        dataVec.clear();
    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    bool insert(int val) {
        if(dataMap.count(val)!=0) return false;
        dataVec.push_back(val);
        dataMap[val]=dataVec.size()-1;
        return true;
    }

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if(dataMap.count(val)==0) return false;
        //existed
        int endData = dataVec[dataVec.size()-1];
        int valLoc = dataMap[val];
        int endLoc = dataMap[endData];

        dataVec[valLoc] = dataVec[endLoc];
        dataMap[endData] = valLoc;
        dataMap[val] = endLoc;

        dataMap.erase(val);
        dataVec.pop_back();
        return true;
    }

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