POJ 1286 Necklace of Beads Polya .

题目地址：http://poj.org/problem?id=1286

旋转+翻转，裸的算法

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
typedef long long LL;
int gcd(int a,int b)
{if(b==0) return a;return gcd(b,a%b);
}
int euler_phi(int n)
{int res=1;for(int i=2;i*i<=n;i++)if(n%i==0) {         //说明i|nn/=i,res*=i-1;while(n%i==0) n/=i,res*=i;  //说明i^2|n}if(n>1) res*=n-1;return res;
}
LL polya(int n)
{LL tot=0;  //方案数 for(int i=1;i<=n;i++)tot+=pow(3,gcd(n,i));tot/=n;	if(n%2!=0) tot+=pow(3,(n+1)/2); //oddelse tot+=(pow(3,n/2)+pow(3,n/2+1))/2;return tot/2;
}
int main()
{int n;while(cin>>n&&n!=-1)if(n==0) cout<<0<<endl;else cout<<polya(n)<<endl;return 0;
}