hihoCoder #1142 : 三分求极值

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 double a,b,c;
 4 const double eps=1e-4;
 5 const double minn=-200;
 6 const double maxn=200;
 7 double x,y;
 8 double solve(double X)
 9 {
10     return sqrt((X-x)*(X-x)+(a*X*X+b*X+c-y)*(a*X*X+b*X+c-y));
11 }
12 int main()
13 {
14   while(scanf("%lf%lf%lf%lf%lf",&a,&b,&c,&x,&y)!=EOF)
15   {
16       double l=minn,r=maxn,midx,midy;
17       while(r-l>eps)
18       {
19           midx=(l+l+r)/3;
20           midy=(l+r+r)/3;
21           if(solve(midx)<=solve(midy))
22             r=midy;
23           else l=midx;
24       }
25       printf("%.3lf\n",solve(l));
26   }
27   return 0;
28 }