[Polya] POJ 2409 Let it Bead

水题...

#include<cstdio>#include<algorithm>using namespace std;typedef long long ll;ll Gcd(ll a,ll b){return b?Gcd(b,a%b):a;}inline ll Pow(ll a,ll b){ll ret=1;for (;b;b>>=1,a*=a)if (b&1)ret*=a;return ret;}int main(){ll c,n,ans;freopen("t.in","r",stdin);freopen("t.out","w",stdout);while (1){scanf("%lld%lld",&c,&n);if (!n && !c) break;ans=0;for (int i=1;i<=n;i++)ans+=Pow(c,Gcd(n,(ll)i));if (n&1)ans+=n*Pow(c,(n+1)>>1);elseans+=n/2*Pow(c,n/2)+n/2*Pow(c,n/2+1);printf("%lld\n",ans/2/n);}return 0;}