左神基础班-randomPool

//等概率返回容器中的东西
#include<iostream>
#include<unordered_map>
#include<ctime>
#include<cstdlib>
using namespace std;
class RandomPool{
private:
	unordered_map<char, int> key2index;
	unordered_map<char, int> index2key;
	int size;
public:
	RandomPool(){
		size =0;
	}
	void add(char c){
		key2index.insert(make_pair(c,size));
		index2key.insert(make_pair(size,c));
		size++;
	}
	void Delete(char key){
		if(!key2index.count(key)){
			return ;
		}
		int lastindex = --size;
		int deleteIndex = key2index.find(key)->second;
		char lastkey = index2key.find(lastindex)->second;
		index2key[deleteIndex] = lastkey;
		index2key.erase(lastindex);
		key2index[lastkey]=deleteIndex;
		key2index.erase(key);
	}
	char getRandom(){
		srand((unsigned int)time(0));
		return index2key[rand() % size];
	}
};
int main(){
	RandomPool pool;
	pool.add('a');
	pool.add('b');
	pool.add('c');
	pool.add('d');

	cout << pool.getRandom() <<endl;
	cout << pool.getRandom() <<endl;
	pool.Delete('a');
	cout << pool.getRandom() <<endl;
	cout << pool.getRandom() <<endl;
}