hdu 1969二分答案

算水题吧，不过这题精度卡得还是挺厉害的，刚开始的时候我是把面积都放大，放大100000000倍，都用long long进行处理，还是过不了，只能用double控制精度了。

/*

 * hdu1969/win.cpp

 * Created on: 2012-11-2

 * Author    : ben

 */

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <cmath>

#include <ctime>

#include <iostream>

#include <algorithm>

#include <queue>

#include <set>

#include <map>

#include <stack>

#include <string>

#include <vector>

#include <deque>

#include <list>

#include <functional>

#include <numeric>

#include <cctype>

using namespace std;

const double eps = 0.000001;

const double pi = acos(-1);

const int MAXN = 10009;

int N, F;

double data[MAXN];



inline bool judge(double ans) {

    int t = 0;

    for(int i = 0; i < N; i++) {

        t += (int)(data[i] / ans);

    }

    return t >= F;

}



double getans() {

    double low = 0, mid;

    double high = *max_element(data, data + N);

    while(high - low > eps) {

        mid = (low + high) / 2;

        if(judge(mid)) {

            low = mid;

        }else {

            high = mid;

        }

    }

    return mid;

}



int main() {

#ifndef ONLINE_JUDGE

    freopen("data.in", "r", stdin);

#endif

    int T, a;

    scanf("%d", &T);

    while(T--) {

        scanf("%d%d", &N, &F);

        F++;

        for(int i = 0; i < N; i++) {

            scanf("%d", &a);

            data[i] = pi * a * a;

        }

        printf("%.4f\n", getans());

    }

    return 0;

}