toxophily.cpp

第四届百度杯编程大赛final解题报告+标程

/**********************************************************************
Author: WHU_dzs
Created Time:  2009-2-15 15:19:13
File Name: pro3.cpp
Description: 
**********************************************************************/
#include <iostream>
#include <cmath>

using namespace std;

double x, y, v;

const double g = 9.8;
const double eps = 1E-9;
const double pi = acos(-1.0);

double calc (double theta) {
	return x * tan(theta) - (g * x * x) / (2 * v * v * cos(theta) * cos(theta));
}

int main () {
    int ca;
    scanf("%d", &ca);
    while (ca--) {
	    scanf ("%lf %lf %lf", &x, &y, &v);
		double low = 0.0, high = pi / 2;
		while (high - low > eps) {
			double mid0 = low  + (high - low) / 3;
			double mid1 = high - (high - low) / 3;
			if (calc(mid0) > calc(mid1))
				high = mid1;
			else
				low  = mid0;
		}
		double max_theta = low;
		double max_y = calc(max_theta);
		if (max_y < y)
			printf ("-1\n");
		else if (fabs(max_y - y) < eps)
			printf ("%.6lf\n", max_theta);
		else {
			low = 0.0, high = max_theta;
			while (high - low > eps) {
				double mid = (high + low) / 2;
				if (calc(mid) > y)
					high = mid;
				else
					low = mid;
			}
            double ans1 = low;
			low = max_theta, high = pi / 2;
			while (high - low > eps) {
				double mid = (high + low) / 2;
				if (calc(mid) < y)
					high = mid;
				else
					low = mid;
			}
            double ans2 = low;
			printf ("%.6lf\n", min(ans1, ans2));
		}
	}
	return 0;
}