Problem - D - Codeforces Fix a Tree

#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn = 2e5+5;
int cur[maxn];
int pre[maxn];
int Find(int x) {return pre[x] == x ? x : Find(pre[x]);}
int main()
{
    int n;
    scanf("%d",&n);
    int thread = 0;
    int ans = 0;
    for(int i = 1; i<=n; i++) pre[i] = i;
    for(int i = 1; i<=n; i++)
    {
        scanf("%d",&cur[i]);
        if(cur[i]==i)
        {
            thread = i;
            ans++;
        }
        else
        {
            int fx = Find(i);
            int fy = Find(cur[i]);
            if(fx == fy)
            {
                cur[i] = i;
                ans++;
            }
            else
            {
                pre[fx] = fy;
            }
        }
    }
    if(thread==0) //全是环
    {
        for(int i = 1; i<=n; i++)
        {
            if(cur[i]==i)
            {
                thread = i;
                break;
            }
        }
        ans++;
    }
    printf("%d\n",ans-1);
    for(int i = 1; i<=n; i++)
    {
        if(cur[i]==i) cur[i] = thread;
    }
    for(int i = 1; i<n; i++) printf("%d ",cur[i]);
    printf("%d\n",cur[n]);
    return 0;
}