BZOJ 2876 【NOI2012】 骑行川藏

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define File(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
#define N 10010
#define eps 1e-12

using namespace std;
typedef long double llg;

int n;
llg E,s
,k
,v1
,v
,maxv
;

void read(llg &x){
double a;
scanf("%lf",&a); x=a;
}

bool check(llg x){
llg l,r,mid,now=0;
for(int i=1;i<=n;i++){
l=max(v1[i]+eps,(llg)0.0); r=maxv[i];
while(r-l>=eps){
mid=(r+l)*0.5;
if(x*k[i]*mid*mid*(mid-v1[i])>=-0.5) l=mid;
else r=mid;
}
v[i]=l; now+=k[i]*(l-v1[i])*(l-v1[i])*s[i];
}
return now<=E;
}

int main(){
File("bicycling");
scanf("%d",&n); read(E);
for(int i=1;i<=n;i++){
read(s[i]),read(k[i]),read(v1[i]);
if(s[i]<=eps){i--,n--;continue;}
maxv[i]=sqrt(E/k[i]/s[i])+v1[i];
}
llg l=-3,r=-eps,mid;
while(r-l>=eps){
mid=(r+l)*0.5;
if(check(mid)) l=mid;
else r=mid;
}
check(l); llg ans=0;
for(int i=1;i<=n;i++) ans+=s[i]/v[i];
printf("%.9lf",(double)ans);
return 0;
}