POJ 1905 Expanding Rods 二分答案几何

题目：http://poj.org/problem?id=1905

恶心死了，POJ的输出一会要lf，一会要f，而且精度1e-13才过，1e-12都不行，错了一万遍终于对了。

 1 #include <stdio.h>

 2 #include <math.h>

 3 

 4 int main()

 5 {

 6     double l, n, c, r;

 7     while(scanf("%lf %lf %lf", &l, &n, &c) != EOF)

 8     {

 9         if(l < 0 && n < 0 && c < 0)break;

10         double arc = (1 + n*c) * l;

11         double low = 0, high = acos(-1.0) / 2;

12         while(high-low > 1e-13)

13         {

14             double mid = (high+low) / 2;

15             r = l/2 / sin(mid);

16             if(r * mid < arc / 2)

17             {

18                 low = mid;

19             }

20             else

21             {

22                 high = mid;

23             }

24         }

25         printf("%.3lf\n", r-r*cos(low));

26     }

27     return 0;

28 }

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