HDU4259(简单群置换)

题目：Double Dealing

#include <iostream>
#include <string.h>

#define LL long long
const int N=1005;

int n,k;
int a[N][N];
bool f[N];
int num[N];

LL gcd(LL a,LL b)
{
    return b? gcd(b,a%b):a;
}

int main()
{
    int i,j;
    while(std::cin>>n>>k)
    {
        if(n==0&&k==0) break;
        if(n<k)
        {
            std::cout<<"1"<<std::endl;
            continue;
        }
        int m=1;
        for(i=1;i<=k&&i<=n;i++)
        for(j=(n-i)/k*k+i;j>0;j-=k)
        num[m++]=j;
        int x;
        LL res=1;
        memset(f,false,sizeof(f));
        for(i=1;i<=n;i++)
        {
            x=i;
            if(f[i]) continue;
            int count=0;
            while(1)
            {
                f[x]=true;
                x=num[x];
                count++;
                if(x==i) break;
            }
            res=res/gcd(res,count)*count;
        }
        std::cout<<res<<std::endl;

    }
    return 0;
}