HDU 5432 Pyramid Split

题意：有n个底面是正方形的四棱锥，用一个水平截面将所有四棱锥分成两半，要求上一半体积的和等于下一半，求水平截面的高度，输出整数部分。

 

解法：二分截面高度。比赛的时候二分写不明白了orz……

 

代码：

#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
#include<math.h>
#include<limits.h>
#include<time.h>
#include<stdlib.h>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<vector>
#define LL long long
using namespace std;
double const eps = 1e-3;
double a[10005], b[10005];
int n;
int cal(double mid)
{
    double sum1 = 0.0, sum2 = 0.0;
    for(int i = 0; i < n; i++)
    {
        if(mid > a[i])
        {
            sum2 += a[i] * b[i] * b[i] / 3.0;
            continue;
        }
        double vsum = a[i] * b[i] * b[i] / 3.0;
        double x = (a[i] - mid) * b[i] / a[i];
        double lvsum = (a[i] - mid) * x * x / 3.0;
        sum1 += lvsum;
        sum2 += vsum - lvsum;
    }
    if(fabs(sum1 - sum2) < eps) return 0;
    if(sum1 > sum2) return 1;
    return -1;
}
int solve()
{
    double l = 0.0, r = 1000.0;
    double mid;
    while((r-l)>= eps)
    {
        mid = (l + r) / 2.0;
        int tmp = cal(mid);
        if(tmp == 0) return mid;
        else if(tmp == 1) l = mid + eps;
        else r = mid - eps;
    }
    return mid;
}
int main()
{
    int T;
    while(~scanf("%d", &T))
    {
        while(T--)
        {
            scanf("%d", &n);
            for(int i = 0; i < n; i++)
                scanf("%lf", &a[i]);
            for(int i = 0; i < n; i++)
                scanf("%lf", &b[i]);
            printf("%d\n", (int)solve());
        }
    }
    return 0;
}

　　

while(r - l > 1)
{
    LL mid = (l + r) >> 1;
    if(judge(mid)) l = mid;
    else
       r = mid;
}
cout << l << endl;
/*贴一个实验室大神的二分模板*/