USACO section1.3 Mixing Milk 混合牛奶

题目：http://www.wzoi.org/usaco/11%5C302.asp

 

水题。。。。。。。按价格升序后，从头开始选。

 

/*
ID: qiufeih1
PROG: milk
LANG: C++
*/

#include <iostream>
#include <fstream>
#include <cstring>
#include <algorithm>
using namespace std;

const int INF = 1<<30;


struct farmer
{
    int price, num;
}a[5010];


bool Cmp(farmer a, farmer b)
{
    return a.price < b.price;
}
int main()
{
    freopen("milk.in", "r", stdin);
    freopen("milk.out", "w",stdout);
    int n, m;
    int star, end;
    int i, j;
    int ans;
    int count;
    int flag;
    int min, max;
    scanf("%d%d", &n, &m);


        for (i = 0; i < m; i++)
        {
            scanf("%d%d", &a[i].price, &a[i].num);
        }
        
        sort(a, a+m, Cmp);
        
        i = 0;
        ans = 0;
        while (n)
        {
            if (n >= a[i].num)
            {
                ans += a[i].num * a[i].price;
                n -= a[i].num;
            }
            else
            {
                ans += n * a[i].price;
                n = 0;
            }
            i++;
        }

        printf("%d\n", ans);

    return 0;
}