cf#320 Div.2 Problem E Weakness and Poorness

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
using namespace std;
int N;
int A[200005];
double f(double x){
double res=0,s1=0,s2=0;
for(int i=0;i<N;i++){
if(s1<0)s1=A[i]-x;
else s1+=A[i]-x;
if(s2>0)s2=A[i]-x;
else s2+=A[i]-x;
res=max(res,max(fabs(s1),fabs(s2)));
}
return res;
}
int main(){
while(scanf("%d",&N)!=EOF){
for(int i=0;i<N;i++) scanf("%d",&A[i]);
double l=-10000,r=10000,m1,m2,a1,a2,ans=1e233;
for(int i=0;i<128;i++){
m1=l+(r-l)/3;
m2=l+(r-l)/3*2;
a1=f(m1),a2=f(m2);
ans=min(ans,min(a1,a2));
if(a1<a2)r=m2;
else l=m1;
}
printf("%.15lf",ans);
}
return 0;
}