感觉自己三分姿势一直是错的所以来补这题
注意输出就好了
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
const int N=25;
const double eps=1e-12,INF=1e200;
int n,p,Bit[N*4];
double a[N],b[N];
void Print(double x){
long long ans=(long long)x;
int dig=0;
while(ans){dig++;Bit[dig]=ans%10;ans/=10;}
ans=(long long)x;
if(dig>=p){
for(int i=dig;i>=dig-p+1;i--)putchar(Bit[i]+'0');
for(int i=dig-p;i>=1;i--)putchar('0');
}
else {
printf("%lld.",ans);
x-=ans;
p-=dig;
while(p--){x*=10;putchar(((long long)x)%10+'0');}
}
putchar('\n');
}
double Score(int x,double diff,double disc){
return 100.0/(1.0+exp(diff-disc*a[x]));
}
double Dec(double diff,double disc){
double ans=0.0;
for(int i=1;i<=n;i++){
double Sc=Score(i,diff,disc);
if(Sc<eps || Sc+eps>=100.0)return INF;
ans+=b[i]*log(100.0/Sc)+(100.0-b[i])*log(100.0/(100.0-Sc));
}
return ans;
}
double Div3_2(double diff){
double l=0.0,r=1.0;
while(r-l>eps){
double mid1=(l+r)/2,mid2=(mid1+r)/2;
if(Dec(diff,mid1)>Dec(diff,mid2))l=mid1;
else r=mid2;
}
return Dec(diff,(l+r)/2);
}
void Div3(){
double l=0.0,r=10.0;
while(r-l>eps){
double mid1=(l+r)/2,mid2=(mid1+r)/2;
if(Div3_2(mid1)>Div3_2(mid2))l=mid1;
else r=mid2;
}
Print(Div3_2((l+r)/2));
}
int main(){
freopen("3330.in","r",stdin);
freopen("3330.out","w",stdout);
scanf("%d %d",&n,&p);
for(int i=1;i<=n;i++)scanf("%lf",&a[i]);
sort(a+1,a+n+1);
for(int i=1;i<=n;i++)b[i]=100.0*(i-1)/(n-1);
Div3();
return 0;
}
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