POJ 2976 Dropping tests [二分]

1.题意：同poj3111，给出一组N个有价值a，重量b的物品，问去除K个之后，剩下的物品的平均值最大能取到多少？

2.分析：二分平均值，注意是去除K个，也就是选取N-K个

3.代码：

# include <iostream>
# include <cstdio>
# include <cmath>
# include <algorithm>
using namespace std;
const int MAXN=1005;
const double eps=1e-8;
int N,K;
int sgn(double x)
{
    if(fabs(x)<eps) return 0;
    if(x<0) return -1;
    else return 1;
}
struct Test
{
    double a,b;
    Test(){}
    Test(double aa,double bb)
    {
        a=aa;
        b=bb;
    }
}T[MAXN];
void Init()
{
    for(int i=0;i<N;i++)
        scanf("%lf",&T[i].a);
    for(int i=0;i<N;i++)
        scanf("%lf",&T[i].b);
}
void Solve()
{
    double temp[MAXN];
    double sum;
    double l=0.0;
    double r=2.0;
    while(sgn(r-l)!=0)
    {
        double mid=l+(r-l)/2.0;
        for(int i=0;i<N;i++)
            temp[i]=mid*T[i].b-T[i].a;
        sort(temp,temp+N);    
        sum=0;
        for(int i=0;i<N-K;i++)
            sum+=-temp[i];
        //printf("%lf %lf
",mid,sum);
        if(sgn(sum)<0) r=mid;
        else l=mid;
    }
    printf("%0.f
",100.0*l);
}
int main()
{
    while(scanf("%d%d",&N,&K)!=EOF)
    {
        if(N==0&&K==0) break;
        Init();
        Solve();
    }
    return 0;
}