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();
*/