10341 - Solve It (UVa)

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

const double eps  = 1e-9;
const double eps2 = 1e-12;
double p, q, r, s, t , u;

double f(double x)
{
    return p*exp(-x) + q*sin(x) + r*cos(x) + s*tan(x) + t*x*x + u;
}
bool flag;
double solve()
{
    double lo=0., hi=1. , mid;
    int it=100;
    if( f(lo)*f(hi)>eps ) {flag = true;return 0;}

    while(it--)
    {
        mid = (lo+hi)/2.;
        int sa,sb;
        if( f(lo) < -eps ) sa = -1;
        else sa = 1;
        if( f(mid) < -eps ) sb = -1;
        else sb = 1;

        if( sa * sb < 0 )
            hi = mid;
        else lo = mid;
    }
    return mid;
}
int main()
{
    //freopen("in.txt", "r", stdin);
    while(scanf("%lf %lf %lf %lf %lf %lf", &p, &q, &r, &s, &t, &u)!=EOF)
    {
        flag= false;
        double n = solve();
        if(flag) printf("No solution\n");
        else printf("%.4lf\n", n);
    }
    return 0;
}