A1489. 抽奖（乔明达）

 1 #include<bits/stdc++.h>
 2 #define maxn 100005
 3 double a[maxn],p[maxn];
 4 double qp(double base,int x){
 5     double ans=1;
 6     while(x){
 7         if(x&1)ans=ans*base;
 8         base=base*base;
 9         x>>=1;
10     }
11     return ans;
12 }
13 int main(){
14     int n,m;
15     scanf("%d%d",&n,&m);
16     int sum=0;
17     for(int i=1;i<=n;i++){
18         scanf("%lf",&a[i]);
19         sum+=a[i];
20     }
21     for(int i=1;i<=n;i++)
22         p[i]=a[i]/sum;
23     double ans1=0;
24     for(int i=1;i<=n;i++)
25         ans1+=p[i]*p[i];
26     ans1=ans1*m*(m-1)+m;
27     double ans2=0;
28     for(int i=1;i<=n;i++)
29         ans2+=qp(1-p[i],m);
30     ans2=n-ans2;
31     printf("%.2lf\n%.2lf\n",ans1,ans2);
32     return 0;
33 }