HDU 2438 (三分)

不知道为什么要加特判才能过～～

#include <bits/stdc++.h>
using namespace std;
#define eps 1e-10
#define pi acos (-1)

double x, y, l, d;

double f (double t) {
    return tan (t)*(-y) + l*sin (t) + d/(cos (t)) - x;
}

double solve () {
    double L = 0.0, R = pi/2.0, LL, RR;
    while (R-L > eps) {
        LL = (2*L+R)/3.0, RR = (2*R+L)/3.0;
        double p1 = f (LL), p2 = f (RR);
        if (p2 >= p1) {
            L = LL;
        }
        else
            R = RR;
    }
    return (L+R)/2.0;
}

int main () {
    //freopen ("in", "r", stdin);
    while (cin >> x >> y >> l >> d) {
        if (d > x || d > y) {
            printf ("no\n");
            continue;
        }
        double ans = solve ();
        if (f (ans) <= eps) {
            printf ("yes\n");
        }
        else
            printf ("no\n");
    }
    return 0;
}