2016夏季练习——二分

来源：POJ1969

二分题

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
const int MAXN = 10010;
const double pi = acos(-1);
const double eps = 1e-6;
int n,f;
double p[MAXN];
int a[MAXN];
bool cmp(double a,double b){
	return a>b;
}
bool judge(double mid){
	int cnt=0;
	for(int i=0;i<n;i++){
		cnt+=(int)(p[i]/mid);
		//cout<<p[i]<<" "<<mid<<" "<<cnt<<endl;
	}
	if(cnt>=f) return 0;
	else return 1;
}
int main(){
	int T;
	scanf("%d",&T);
	while(T--) {
	    scanf("%d%d",&n,&f);
	    f++;
	    double maxn=-1;
	    double sum=0;
	    for(int i=0;i<n;i++){
	    	scanf("%d",&a[i]);
	    	p[i]=a[i]*a[i]*pi;
	    	sum+=p[i];
	    	if(p[i]>maxn) maxn=p[i];
	    }
	    double left=(double)(maxn/(f*1.0));
	    double right=sum*1.0/(1.0*f);
	    sort(p,p+n,cmp);
	    while(right-left>eps){
	    	double mid=(right+left)/2;
	    	if(!judge(mid)){
	    		left=mid;
	    	}
	    	else{
	    		right=mid;
	    	}
	    }
	    printf("%.4f\n",left);
	}
	return 0;
}