HDU ACM 1873 看病要排队 (优先队列priority_queue)

http://acm.hdu.edu.cn/showproblem.php?pid=1873

主要练习优先队列的应用，学会如何重载小于号（operator <）

若用自定义类型应用优先队列时要重载小于号，类比sort函数　　 

#include <iostream>
#include <queue>
#include <string>
using namespace std;
struct FUN
{
    int ID;
    int lv;
    friend bool operator < (const FUN &x,const FUN &y)
    {
        if(x.lv == y.lv)
        {
            return x.ID > y.ID;
        }
        return x.lv < y.lv;
    }
};
int main()
{
    int n;
    while(cin>>n)
    {
        int ID = 1;
        priority_queue <FUN> doc[4];
        FUN sick = {0};
        for(int i=0;i<n;i++)
        {
            string str;
            cin>>str;
            int num;
            if(str == "IN")
            {
                cin>>num;
                sick.ID = ID;
                cin>>sick.lv;
                doc[num].push(sick);
                ID++;
            }
            else
            {
                cin>>num;
                if(!doc[num].empty())
                {
                    cout<<doc[num].top().ID<<endl;
                    doc[num].pop();
                }
                else
                {
                    cout<<"EMPTY"<<endl;
                }
            }
        }
    }
    return 0;
}