Solve It - UVa 10341 二分

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Solve It

Input: standard input

Output: standard output

Time Limit: 1 second

Memory Limit: 32 MB

Solve the equation:
        p*e-x q*sin(x) + r*cos(x) + s*tan(x) + t*x2 + u = 0
        where 0 <= x <= 1.

Input

Input consists of multiple test cases and terminated by an EOF. Each test case consists of 6 integers in a single line: pqrst and u(where 0 <= p,r <= 20 and -20 <= q,s,t <= 0). There will be maximum 2100 lines in the input file.

Output

For each set of input, there should be a line containing the value of x, correct upto 4 decimal places, or the string "No solution", whichever is applicable.

Sample Input

0 0 0 0 -2 1
1 0 0 0 -1 2
1 -1 1 -1 -1 1

Sample Output

0.7071
No solution
0.7554

题意:求上式中0的解x。

思路:二分求解。有一点我很奇怪的是,当eps=1e-6时WA,至少要1e-7,但是答案只需要输出前4位,这点我很无语,求解释。

AC代码如下:

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>using namespace std;double p,q,r,s,t,u,eps=1e-7;double solve(double x){    return p*exp(-x)+q*sin(x)+r*cos(x)+s*tan(x)+t*x*x+u;}int main(){    int n,i,j,k;    double L,R,mi;    while(~scanf("%lf%lf%lf%lf%lf%lf",&p,&q,&r,&s,&t,&u))    {        if(solve(0)*solve(1)>0)        {            printf("No solution\n");            continue;        }        L=0;R=1;        while(R-L>eps)        {            mi=(L+R)/2;            if(solve(mi)*solve(L)>0)              L=mi;            else              R=mi;        }        printf("%.4f\n",L);    }}



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