C++-hihoCoder-1142-三分求极值[三分]

#include <bits/stdc++.h>
using namespace std;
typedef double db;
const db eps=1e-9;
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=-200,r=200,ans1,ans2;
    while(r-l>eps){
        db ll=(2*l+r)/3,rr=(l+2*r)/3;
        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
",third());
    return 0;
}