poj1905

题意：给出膨胀指数，加热温度，杆子的原长度，问加热后的杆子两端点位置不变，弯曲成弧，圆心的位置。

分析：二分答案，二分查找圆心位置，根据圆心位置计算出弧长与原弧长比较，不知道为什么wa那么多次。

View Code

#include < iostream >
#include < cstdio >
#include < cstdlib >
#include < cstring >
#include < cmath >
using namespace std;

#define eps 1.0e-8

double c, l1, n;

double cal( double b)
{
double a = l1 / 2 ;
double d = sqrt(a * a + b * b);
double h = a * d / b;
double r = sqrt(h * h + d * d) / 2 ;
return atan(b / (l1 / 2 )) * 4 * r;
}

int main()
{
// freopen("t.txt", "r", stdin);
while (scanf( " %lf%lf%lf " , & l1, & n, & c) != EOF)
{
if (n < 0 && l1 < 0 && c < 0 )
break ;
double l2 = l1 * (n * c + 1 );
if (l2 - l1 < eps)
{
printf( " 0.000\n " );
continue ;
}
double l = eps;
double r = l1 / 2 ;
double mid;
while (abs(l - r) > eps)
{
mid = (l + r) / 2 ;
double x = cal(mid);
if (abs(x - l2) < eps)
break ;
if (x > l2)
r = mid - eps;
else
l = mid + eps;
}
printf( " %.3f\n " , mid);
}
return 0 ;
}