【POJ】3122 Pie [二分查找]

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
const int N=1e4+11;
const double PI = acos(-1.0);
const double EPS = 1e-6;
int n,m;
double a
;
double INF;

void init()
{
INF=0;
}

int check(double x)
{
int cnt=0;
for(int i=0;i<n;i++){
cnt+=(int)a[i]/x;
}
return cnt;
}
double BinSearch(double* a)
{
double head=0, tail=INF;
double mid;

while(head+EPS<tail){
mid=(head+tail)/2.0;
if(check(mid)<m){
tail=mid;
} else {
head=mid;
}
}
return mid;
}
int main()
{
int T;
scanf("%d",&T);
while(T--){
init();
scanf("%d%d",&n,&m);
m++;
for(int i=0;i<n;i++){
scanf("%lf",&a[i]);
a[i]=a[i]*a[i];
if(a[i]>INF) INF=a[i];
}
printf("%.4f\n",BinSearch(a)*PI);
}

return 0;
}