bzoj2369

answer:

Obviously find each ring

Then do a lcm

Code:

#include<cstdio>
using namespace std;
int a[1005],f[1005],n;
int gcd(int x,int y)
{
    if (!y)return x;
    return gcd(y,x%y);
}
intmain ()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)scanf("%d",&a[i]);
    int ans=1;
    for (int i=1;i<=n;i++)
     if (!f[i]) 
      {
          int j=i,num=0;
          while (j!=i||num==0)
           {
               f[j]=1;
               j=a[j];
               num ++ ;
           }
          ans =ans/gcd(ans,num)* num;
      }
    printf("%d",ans); 
}