XDOJ_1093_二分

Posted 2020-08-15

http://acm.xidian.edu.cn/problem.php?id=1093

 

先以1为区间大小找到含根的区间，然后二分找精确答案。

 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
using namespace std;
const double eps=0.0001;
double a,b,c,d;

double ans[5];
int sum;

inline double calc(double x)
{
    return a*x*x*x+b*x*x+c*x+d;
}

inline void find(double l,double r)
{
    if(r-l <= eps)
    {
        ans[++sum] = (l+r)/2;
        return;
    }
    double mid = (l+r)/2,tmp = calc(mid),tmpl = calc(l),tmpr = calc(r);
    if(abs(tmp) < eps)
    {
        ans[++sum] = mid;
        return;
    }
    if(tmp*tmpl < 0)
    {
        find(l,mid);
        return;
    }
    find(mid,r);
}

int main()
{
    while(~scanf("%lf%lf%lf%lf",&a,&b,&c,&d))
    {
        sum = 0;
        for(int i=-101;i<=101;i++)
        {
            double tmp1 = calc(i),tmp2 = calc(i+1);
            if(abs(tmp1) < eps)    ans[++sum] = i;
            else if(abs(tmp2) < eps)
            {
                ans[++sum] = i+1;
                i++;
            }
            else if(tmp1*tmp2 < 0)    find(i,i+1);
            if(sum == 3)    break;
        }
        sort(ans+1,ans+4);
        printf("%.2lf %.2lf %.2lf\n",ans[1],ans[2],ans[3]);
    }
    return 0;
}