POJ 1286 Necklace of Beads

直接套，n==0时要特判，还有输出结果要用__int64

#include<stdio.h>
#include<math.h>
int gcd(int a,int b) {
	if (b==0) return a;
	else return gcd(b,a%b);
}
int main() {
#ifndef ONLINE_JUDGE
	freopen("in.txt","r",stdin);
#endif
	int n;
	while(scanf("%d",&n)) {
		if (n==0) {
			printf("0\n");
			continue;
		}
		if (n==-1) break;
		int i;pow(
		__int64 ans=0;
		for(i=0;i<n;i++) {
			ans+=pow(3.0,gcd(n,i));
		}
		if (n%2==0) {
			ans+=n/2*pow(3.0,n/2+1);
			ans+=n/2*pow(3.0,n/2);
		} 
		else ans+=n*pow(3.0,n/2+1);
		ans/=2*n;
		printf("%I64d\n",ans);
	}
	return 0;
}