USACO-Section1.4 Mixing Milk （贪心算法）

从拥有不同单价和库存牛奶的M个农场主手里买数量为N的牛奶的最小支出

每次都选择单价最小的

/*
ID: 18795871
PROG: milk
LANG: C++
*/
#include<iostream>
#include<fstream>
#include<cstdlib>
using namespace std;

const int N = 5000;

ifstream fin("milk.in");
ofstream fout("milk.out");

struct ll{
int pri,num;
}x[N+1];

int cmp(const void *a,const void *b){
struct ll *k1=(struct ll*)a;
struct ll *k2=(struct ll*)b;
if (k1->pri==k2->pri) return k1->num-k2->num;
return k1->pri-k2->pri;
}

int main()
{
int i,n,m;
fin>>n>>m;
for (i=1;i<=m;i++){
fin>>x[i].pri>>x[i].num;
}
qsort(x+1,m,sizeof(x[0]),cmp);
int sum=0;
for (i=1;i<=m;i++){
int r=min(n,x[i].num);
sum+=r*x[i].pri;
n-=r;
if (n<=0) break;
}
fout<<sum<<endl;
return 0;
}

/*
ID: 18795871
PROG: milk
LANG: C++
*/
#include<iostream>
#include<fstream>
#include<algorithm>
using namespace std;

ifstream fin("milk.in");
ofstream fout("milk.out");

const int N = 5000;
int n,m;

struct nn{
int p,a;
}x[N+1];

bool cmp(struct nn t1,struct nn t2){
return t1.p<t2.p;
}

int main(){
while (fin>>n>>m){
for (int i=0;i<m;i++){
fin>>x[i].p>>x[i].a;
}
sort(x,x+m,cmp);
int sum=0;
for (int i=0;i<m;i++){
int cnt=min(x[i].a,n);
sum+=cnt*x[i].p;
n-=cnt;
if (n<=0) break;
}
fout<<sum<<endl;
}
return 0;
}