[USACO 1.3.1]混合牛奶 (贪心法)

#include <stdio.h>
#include <stdlib.h>

struct milksuply
{
int cost;
int num;
}suply[5005];

int cmp(const void *a,const void *b)
{
return ((milksuply *)a)->cost-((milksuply *)b)->cost;
}

int main()
{
int n,m;
scanf("%d%d",&n,&m);
for(int i=0;i<m;i++)
{
scanf("%d%d",&suply[i].cost,&suply[i].num);
}
qsort(suply,m,sizeof(milksuply),cmp);

int sum=0;
int ans=0;
for(int i=0;i<m;i++)
{
if(sum+suply[i].num>n)
{
ans+=(n-sum)*suply[i].cost;
break;
}
else
{
sum+=suply[i].num;
ans+=suply[i].num*suply[i].cost;
}
}
printf("%d\n",ans);
}