[UVa] 12079 Pie.cpp

#include <cstdio>
#include <cmath>
using namespace std;
int main()
{
    const double pi = 2 * asin(1);
    int Case,N, F;
    int R[10001];
    scanf("%d",&Case);
    while (Case--){
        scanf("%d%d", &N, &F);
        F++;
        int UP = 0;  // BS上界
        for (int i=0; i<N; i++){
            scanf("%d",&R[i]);
            R[i] *= R[i];
            if (R[i] > UP) UP = R[i];
        }
        double left = 0, right = UP;
        while (right-left > 0.00000001){
            double mid = (left+right)/2;
            int piece = 0;
            for (int i=0; i<N; i++)
                piece += R[i]/mid;
            if (piece >= F) left = mid; //片數大於人數 因此往上逼近
            else right = mid;
        }
        printf("%.3f\n",pi * left);
    }
    return 0;
}