C++-hihoCoder-1142-三分求极值[三分]

 #include <bits/stdc++.h>
 using namespace std;
 typedef double db;
 const db eps=1e-;
 db a,b,c,x,y;
 db dis2(db X){
     db Y=a*X*X+b*X+c;
     return (X-x)*(X-x)+(Y-y)*(Y-y);
 }
 db third(){
     db l=-,r=,ans1,ans2;
     while(r-l>eps){
         db ll=(*l+r)/,rr=(l+*r)/;
         ans1=dis2(ll);ans2=dis2(rr);
         ans1<ans2?r=rr:l=ll;
     }
     return sqrt(ans1);
 }
 int main(){
     scanf("%lf%lf%lf%lf%lf",&a,&b,&c,&x,&y);
     printf("%.3f\n",third());
     return ;
 }