698B - Fix a Tree - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
int n,a[200001],b[200001],c[200001],r,g;
int dfs(int x){
	if(c[x])return c[x];
	if(b[x])return c[x]=x;
	b[x]=1;
	return c[x]=dfs(a[x]);
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i];
	for(int i=1;i<=n;i++)dfs(i);
	for(int i=1;i<=n;i++)if(a[i]==i&&c[i]==i)r=i;
	if(!r){
		for(int i=1;i<=n;i++){
			if(c[i]!=i)continue;
			g++;
			a[i]=r=i;
			break;
		}
	}
	for(int i=1;i<=n;i++)if(c[i]==i)g++,a[i]=r;
	cout<<g-1<<endl;
	for(int i=1;i<=n;i++)cout<<a[i]<<' ';
	return 0;
}