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;}