DFS USING STACK

#include <bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL)
#define ll long long
#define ld long double
#define pb push_back
#define fe first
#define se second
#define st(x) sort(x.begin(),x.end())
#define rst(x) sort(x.rbegin(),x.rend())
const long double pi = 3.14159265358979323;
const double EPS = 1e-12;
const int N = 1e6 + 5;
const int mod = 1e9 + 7;
vector<ll>v[N];
bool visit[N];
void dfs(int p)
{
    stack<int>s;
    s.push(p);
    visit[p]=1;
    while(!s.empty())
    {
        int x=s.top();
        s.pop();
    for(auto it:v[x])
    {
        if(!visit[it])
        {
         // dfs(v[p][i]);
         visit[it]=1;
         s.push(it);
        }
    }
}
}
int main()
{
    fast;
    ll n,a,c=0;
    cin>>n;
    for(int i=1;i<=n;i++){
    cin>>a;
    v[i].pb(a);
    v[a].pb(i);
    }
    for(int i=1;i<=n;i++)
    {
        if(!visit[i]){
            dfs(i);
        c++;
        }
    }
    cout<<c;
    return 0;
}