【hdu2199】Can you solve this equation?——二分

题目:

Can you solve this equation?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 15110    Accepted Submission(s): 6739


Problem Description
Now,given the equation 8*x^4 + 7*x^3 + 2*x^2 + 3*x + 6 == Y,can you find its solution between 0 and 100;
Now please try your lucky.
 

Input
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has a real number Y (fabs(Y) <= 1e10);
 

Output
For each test case, you should just output one real number(accurate up to 4 decimal places),which is the solution of the equation,or “No solution!”,if there is no solution for the equation between 0 and 100.
 

Sample Input
2 100 -4
 

Sample Output
1.6152 No solution!
 

Author
Redow

描述:求方程的解

题解:二分裸题

代码:

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
using namespace std;
const double eps = 1e-10;
double f(double x)
{
	return 8.0 * pow(x,4) + 7 * pow(x,3) + 2 * pow(x,2) + 3 * x + 6;
}
int main()
{
	//freopen("input.txt", "r", stdin);
	int T;
	scanf("%d", &T);
	while (T--)
	{
		double Y;
		scanf("%lf", &Y);
		double l = 0.0;
		double r = 100.0;
		if (f(l) > Y || f(r) < Y)
		{
			printf("No solution!\n");
			continue;
		}
		while (r - l > eps)
		{
			double mid = (l + r) / 2;
			if (f(mid) > Y)
				r = mid;
			else
				l = mid;
		}
		printf("%.4lf\n", r);
	}

	return 0;
}


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