POJ 1905 Expanding Rods

Description

When a thin rod of length L is heated n degrees, it expands to a new length L‘=(1+n*C)*L, where C is the coefficient of heat expansion. 
When a thin rod is mounted on two solid walls and then heated, it expands and takes the shape of a circular segment, the original rod being the chord of the segment. 

Your task is to compute the distance by which the center of the rod is displaced. 

Input

Output

Sample Input

1000 100 0.0001
15000 10 0.00006
10 0 0.001
-1 -1 -1

Sample Output

61.329
225.020
0.000

Source

1

#include <iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
#define maxn 25100000
#define inf 0x3f3f3f3f
#define pi acos(-1.0)
#define eps 1e-7
double l,n,c;
double a,r;
bool ok(double a){
   if(l/sin(a)*a<(1+n*c)*l)return true;
   else return false;
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(~scanf("%lf%lf%lf",&l,&n,&c)){
        if(l==-1||n==-1||c==-1)break;
           double ua=0;
           double ub=pi/2;
           double mid;
           /*
        while((ub-ua)>eps){
            mid=(ub+ua)/2;
            if(ok(mid))ua=mid;
            else ub=mid;
        }
        */
        
        for(int i=0;i<100;i++){
            mid=(ua+ub)/2;
            if(ok(mid))ua=mid;
            else ub=mid;
        }
        printf("%.3f\n",l/2/sin(mid)*(1-cos(mid)));
    }
}

转自http://blog.csdn.net/u013748887/article/details/24369543

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
const double esp=1e-5;//最小精度
int main()
{
    double L,n,c,s;
    double h;
    double r;
    double mid;
    while(scanf("%lf%lf%lf",&L,&n,&c)!=EOF)
    {
        if(L==-1&&n==-1&&c==-1)
        break;
        double low=0;
        double high=0.5*L;
        double mid;
        s=(1+n*c)*L;
        while(high-low>esp)//这里不能直接用hign>low,否则当low与high很接近时会陷入死循环
        {
            mid=(high+low)/2;
            r=(4*mid*mid+L*L)/(8*mid);
            if(2*r*asin(L/(2*r))<s)
            low=mid;
            else high=mid;
        }
        h=mid;
        printf("%.3lf\n",h);
    }
    return 0;
}

POJ 1905 Expanding Rods

原文：http://blog.csdn.net/u013497977/article/details/44901005