LA 3635 Pie

题意：给出n个圆，分给n+1个人，求每个人最多能够得到多大面积的圆

二分每个人得到的圆的面积

#include<iostream>  
#include<cstdio>  
#include<cstring> 
#include <cmath> 
#include<stack>
#include<vector>
#include<map> 
#include<set>
#include<queue> 
#include<algorithm>  
using namespace std;

typedef long long LL;
const int INF = (1<<30)-1;
const int mod=1000000007;
const int maxn=1000005;
const double pi = 3.14159265359;

double a[maxn];
int n,f;

int ok(double x){
    int ans = 0;
    for(int i = 1;i <= n;i++){
        ans += (int) (a[i] / x);
    }
    return ans >= f+1;
}

int main(){
    int T;
    scanf("%d",&T);
    while(T--){
        scanf("%d %d",&n,&f);
        double lb,ub,mid;
        ub = -1;
        for(int i =1;i <= n;i++){
            scanf("%lf",&a[i]);
            a[i] = a[i] * a[i];
            ub = max(ub,a[i]);
        }
         
         lb = 0.000;
        for(int i = 0;i<=100;i++){
            mid = (lb + ub) / 2;
            if(ok(mid)) lb = mid;
            else ub = mid;
        //    printf("lb = %lf  ub = %lf  mid = %lf
",lb,ub,mid);
        }
        printf("%.4lf
",lb * pi);
    }
    return 0;
}