USACO 1.3.1

题目链接:USACO 1.3.1

简单的贪心,将cent从小到大排序.

/*
ID:wang9621
PROG:milk
LANG:C++
*/
#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
struct edge
{
    int cent;
    int unit;
};
edge per[];
bool cmp(edge a,edge b)
{
    return a.cent<b.cent;
}
int main()
{
    freopen("milk.in","r",stdin);
    freopen("milk.out","w",stdout);
    int n,m;
    scanf("%d %d",&n,&m);
    for(int i = ; i<=m; i++)
    {
        scanf("%d %d",&per[i].cent,&per[i].unit);
    }
    sort(per+,per+m+,cmp);
    int sum = ;
    for(int i = ; i<=m; i++)
    {
        if(n>=per[i].unit)
        {
            sum += per[i].cent*per[i].unit;
            n -= per[i].unit;
        }
        else if(n>)
        {
            sum += n*per[i].cent;
            n = ;
        }

    }
    printf("%d\n",sum);
    return ;
}