//贪心//从后往前枚举有奇效//Supermarket------二S

A supermarket has a set Prod of products on sale. It earns a profit px for each product x∈Prod sold by a deadline dx that is measured as an integral number of time units starting from the moment the sale begins. Each product takes precisely one unit of time for being sold. A selling schedule is an ordered subset of products Sell ≤ Prod such that the selling of each product x∈Sell, according to the ordering of Sell, completes before the deadline dx or just when dx expires. The profit of the selling schedule is Profit(Sell)=Σ x∈Sellpx. An optimal selling schedule is a schedule with a maximum profit.
For example, consider the products Prod={a,b,c,d} with (pa,da)=(50,2), (pb,db)=(10,1), (pc,dc)=(20,2), and (pd,dd)=(30,1). The possible selling schedules are listed in table 1. For instance, the schedule Sell={d,a} shows that the selling of product d starts at time 0 and ends at time 1, while the selling of product a starts at time 1 and ends at time 2. Each of these products is sold by its deadline. Sell is the optimal schedule and its profit is 80.
Write a program that reads sets of products from an input text file and computes the profit of an optimal selling schedule for each set of products.
Input
A set of products starts with an integer 0 <= n <= 10000, which is the number of products in the set, and continues with n pairs pi di of integers, 1 <= pi <= 10000 and 1 <= di <= 10000, that designate the profit and the selling deadline of the i-th product. White spaces can occur freely in input. Input data terminate with an end of file and are guaranteed correct.
Output
For each set of products, the program prints on the standard output the profit of an optimal selling schedule for the set. Each result is printed from the beginning of a separate line.
Sample Input
4 50 2 10 1 20 2 30 1
7 20 1 2 1 10 3 100 2 8 2
5 20 50 10
Sample Output
80
185
Hint
The sample input contains two product sets. The first set encodes the products from table 1. The second set is for 7 products. The profit of an optimal schedule for these products is 185.

解题思路：
emmmmm…
其实一开始感觉和背包的感觉有点像，所以就想到一天一天的枚举，保证每一天卖出的产品获利都是最大的。
但是发现如果从第一天往后推就很麻烦，因为第一天可以卖所有产品，依次往后选择越来越少。
如果反向思考，从最后一天往前推就简单很多，最后一天可以选择的只有deadline在最后一天的产品，依次往前推可以用优先队列把利益最大的pop出来。

#include<stdio.h>
#include<queue>
#include<algorithm>
using namespace std;

struct node
{
    int p;
    int d;
    friend bool operator < (node x,node y)
    {
        if(x.p!=y.p) return x.p<y.p;//优先队列中先pop利益最大的
    }
}pro[10010];

bool cmp (node x,node y)
{
    if(x.d!=y.d) return x.d>y.d;
}

int main()
{
    int n,dl,i,j,ans,temp;
    while(scanf("%d",&n)!=EOF)
    {
        dl=0;
        for(i=1;i<=n;i++)
        {
            scanf("%d%d",&pro[i].p,&pro[i].d);
            pro[i].d>dl?dl=pro[i].d:dl=dl;
        }
        sort(pro+1,pro+n+1,cmp);//按照deadline从大到小排序
        j=1;
        ans=0;
        priority_queue<int> q;
        for(i=dl;i>=1;i--)
        {
            while(pro[j].d>=i)
            {
                q.push(pro[j].p);
                j++;
            }
            if(q.empty()==false)
            {
                ans+=q.top();
                q.pop();
            }
        }
        printf("%d\n",ans);
    }
}