poj1905 Expanding Rods

精度限定到1e-12即可。

http://poj.org/problem?id=1905

#include <cstdio>
#include <cmath>

using namespace std;

const double pi = 3.14159265359;
const double ep = 1e-12;

double l, n, c;

void solve(){
    double low = ep, high = pi / 2;
    double l1 = (1 + n * c) * l;
    double d1, d2, mid;
    d2 = l / l1;
    while(high - low > ep){
        mid = (low + high) / 2;
        d1 = sin(mid) / mid;
        if(d1 > d2) low = mid;
        else high = mid;
    }
    d1 = sin(low), d2 = sin(low / 2);
    printf("%.3f
", l * d2 * d2 / d1);
}

int main(){
    //freopen("in.txt", "r", stdin);
    while(~scanf("%lf%lf%lf", &l, &n, &c) && (l + 1)){
        solve();
    }
    return 0;
}