poj2369

简单题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 1005

int f[maxn];
int n;
bool vis[maxn];

int gcd(int x, int y)
{
    if (!x || !y)
        return x > y ? x : y;
    for (int t; t = x %y; x = y, y = t);
    return y;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d", &n);
    for (int i = 0; i< n; i++)
    {
        int a;
        scanf("%d", &a);
        a--;
        f[a] = i;
    }
    memset(vis, 0, sizeof(vis));
    int ans = 1;
    for (int i = 0; i < n; i++)
        if (!vis[i])
        {
            int a = i;
            int b = 0;
            while (!vis[a])
            {
                vis[a] = true;
                a = f[a];
                b++;
            }
            ans = ans / gcd(ans, b) * b;
        }
    printf("%d\n", ans);
    return 0;
}