51nod 1257 背包问题 V3

分数规划。

#include<bits/stdc++.h>
using namespace std;

const int MAXN=50050;
long long resw,resp;
int n,k;

struct node
{
int w,p;
double rate;
}a[MAXN];

bool cmp(node n1,node n2)
{
return n1.rate>n2.rate;
}

bool judge(double p)
{
int i;
double mark;
resw=0;
resp=0;
mark=0;
for(i=1;i<=n;i++)
a[i].rate=a[i].p-a[i].w*p;
sort(a+1,a+n+1,cmp);
for(i=1;i<=k;i++)
{
resw+=a[i].w;
resp+=a[i].p;
mark+=a[i].rate;
}
if(mark>=0)
return 1;
else
return 0;
}

int main()
{
int i;
double lef,rig,mid;
long long tmp,answ,ansp;
while(~scanf("%d%d",&n,&k))
{
for(i=1;i<=n;i++)
{
scanf("%d%d",&a[i].w,&a[i].p);
}
lef=0;
rig=50050;
for(i=0;i<100;i++)
{
mid=(lef+rig)/2;
if(judge(mid))
{
answ=resw;
ansp=resp;
lef=mid;
}
else
rig=mid;
}
tmp=__gcd(answ,ansp);
printf("%lld/%lld\n",ansp/tmp,answ/tmp);
}
}