Codeforces Round #259 (Div. 2) C. Little Pony and Expected Maximum (找规律)
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题目链接:Codeforces Round #259 (Div. 2) C. Little Pony and Expected Maximum
求M面的骰子扔N次的最大点数的期望。
找规律。
6 3
E=1
111
N==1
E=2
112 121 211
122 212 221
222
N=7=2^n-1^n
E=3
113 131 311
223 232 322
123 132 213 231 321 312
133 331 313
233 332 323
333
N=19=3^n-2^n
......
期望就是:N*E*(1/m)^n,即 i*(i^n-(i-1)^n)*(1/m)^n。化简不然会溢出。i*((i/m)^n-((i-1)/m)^n)
AC代码:
#include<stdio.h>double quick(double n,int p){double m,b;b=1.0;m=n;while(p){if(p%2)b*=m;p/=2;m*=m;}return b;}int main(){int i,j,n,m;double ans;while(scanf("%d%d",&m,&n)!=EOF){ans=1.0*quick(1.0/m,n);for(i=2;i<=m;i++){ans+=i*(quick(1.0*i/m,n)-quick(1.0*(i-1)/m,n));}printf("%lf\n",ans);}return 0;}
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