HDU-2199 二分法

二分法求方程的根

/*
* hdu-2199 can you solve the equatino
* mike-w
* 2012-4-17
*
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#define EPS (1e-6)
#define nDISP_X1_X2

const int co[10]={8,7,2,3,6};

double foo(double x)
{
double x0=co[0];
int i;
for(i=0;i<4;i++)
x0=x*x0+co[i+1];
return x0;
}

double solve(double Y)
{
double x1=0.0, x2=100.0, mid;
double y1=foo(x1), y2=foo(x2);
while(fabs(y1-y2)>EPS)
{
#ifdef DISP_X1_X2
printf("x1,x2 = %lf,%lf\n",x1,x2);
printf("y1,y2 = %lf,%lf\n",y1,y2);
#endif
mid=(x1+x2)/2;
if(foo(mid)>Y)
y2=foo(x2=mid);
else
y1=foo(x1=mid);
}
return x1;
}

int main(void)
{
int T;
double min_v=(double)foo(0);
double max_v=(double)foo(100);
double Y;
scanf("%d",&T);
while(T-->0)
{
scanf("%lf",&Y);
if(Y>max_v || Y<min_v)
printf("No solution!\n");
else
printf("%.4lf\n",solve(Y));
}
return 0;
}