func_code_string: #include <bits/stdc++.h>   using namespace std;   constexpr long long maxn = 2e5 + 5, inf = 0x3f3f3f3f, mod = 1e9 + 7;   long long n, m, du[maxn], vis[maxn], f[maxn];   long long res, ans = 1;   vector<long long> e[maxn];   map<pair<long long, long long>, long long> mp;   inline long long ksm(long long a, long long b) {     long long k = 1;     while (b) {       if (b & 1) k = k * a % mod;       a = a * a % mod;       b >>= 1;     }     return k;   }   void topo() {     queue<long long> q;     for (long long i = 1; i <= n; i++) {       if (du[i] == 1) {         q.push(i);         vis[i] = i;       }     }     while (!q.empty()) {       long long u = q.front();       q.pop();       for (auto v : e[u]) {         du[v]--;         if (du[v] <= 1 && !vis[v]) {           vis[v] = v;           q.push(v);         }       }     }   }   void dfs(long long u, long long fa) {     vis[u] = fa;     f[fa]++;     for (auto v : e[u]) {       if (!vis[v] && du[v] > 1) {         dfs(v, fa);       }     }   }   signed main() {     cin >> n;     long long flag = 0;     for (long long i = 1; i <= n; i++) {       long long x;       cin >> x;       e[i].emplace_back(x);       e[x].emplace_back(i);       du[i]++;       du[x]++;     }     topo();     for (long long i = 1; i <= n; i++) {       if (!vis[i] && du[i] > 1) {         dfs(i, i);       }     }     for (long long i = 1; i <= n; i++) {       if (vis[i] == i && f[i] == 0) {         res++;       } else if (vis[i] == i && f[i] > 1) {         ans = ans * (ksm(2, f[i]) - 2) % mod;       }     }     cout << ans * ksm(2, res) % mod;   }   