1 #include <algorithm>  2 #include <iostream>  3 #include <iomanip>  4 #include <cstring>  5 #include <climits>  6 #include <complex>  7 #include <fstream>  8 #include <cassert>  9 #include <cstdio> 10 #include <bitset> 11 #include <vector> 12 #include <deque> 13 #include <queue> 14 #include <stack> 15 #include <ctime> 16 #include <set> 17 #include <map> 18 #include <cmath> 19 using namespace std; 20 #define fr first 21 #define sc second 22 #define cl clear 23 #define BUG puts("here!!!") 24 #define W(a) while(a--) 25 #define pb(a) push_back(a) 26 #define Rint(a) scanf("%d", &a) 27 #define Rll(a) scanf("%I64d", &a) 28 #define Rs(a) scanf("%s", a) 29 #define Cin(a) cin >> a 30 #define FRead() freopen("in", "r", stdin) 31 #define FWrite() freopen("out", "w", stdout) 32 #define Rep(i, len) for(int i = 0; i < (len); i++) 33 #define For(i, a, len) for(int i = (a); i < (len); i++) 34 #define Cls(a) memset((a), 0, sizeof(a)) 35 #define Clr(a, x) memset((a), (x), sizeof(a)) 36 #define Full(a) memset((a), 0x7f7f7f, sizeof(a)) 37 #define lrt rt << 1 38 #define rrt rt << 1 | 1 39 #define pi 3.14159265359 40 #define RT return 41 #define lowbit(x) x & (-x) 42 #define onecnt(x) __builtin_popcount(x) 43 typedef long long LL; 44 typedef long double LD; 45 typedef unsigned long long ULL; 46 typedef pair<int, int> pii; 47 typedef pair<string, int> psi; 48 typedef pair<LL, LL> pll; 49 typedef map<string, int> msi; 50 typedef vector<int> vi; 51 typedef vector<LL> vl; 52 typedef vector<vl> vvl; 53 typedef vector<bool> vb; 54  55 const int maxn = 200200; 56 const LL mod = 1e9+7; 57 LL ret; 58  59 typedef struct Edge { 60     int u; 61     int v; 62     int next; 63     Edge() { next = -1; } 64 }Edge; 65  66 int head[maxn], ecnt; 67 Edge edge[maxn]; 68 int n, m; 69  70 int bcnt, dindex; 71 int dfn[maxn], low[maxn]; 72 int stk[maxn], top; 73 int belong[maxn]; 74 int in[maxn], out[maxn]; 75 bool instk[maxn]; 76 int cnt[maxn]; 77  78 void init() { 79     memset(edge, 0, sizeof(edge)); 80     memset(head, -1, sizeof(head)); 81     memset(instk, 0, sizeof(instk)); 82     memset(dfn, 0, sizeof(dfn)); 83     memset(low, 0, sizeof(low)); 84     memset(belong, 0, sizeof(belong)); 85     memset(in, 0, sizeof(in)); 86     memset(out, 0, sizeof(out)); 87     ecnt = top = bcnt = dindex = 0; 88 } 89  90 void adde(int uu, int vv) { 91     edge[ecnt].u = uu; 92     edge[ecnt].v = vv; 93     edge[ecnt].next = head[uu]; 94     head[uu] = ecnt++; 95 } 96  97 void tarjan(int u) { 98     int v = u; 99     dfn[u] = low[u] = ++dindex;100     stk[++top] = u;101     instk[u] = 1;102     for(int i = head[u]; ~i; i=edge[i].next) {103         v = edge[i].v;104         if(!dfn[v]) {105             tarjan(v);106             low[u] = min(low[u], low[v]);107         }108         else if(instk[v]) low[u] = min(low[u], dfn[v]);109     }110     if(dfn[u] == low[u]) {111         bcnt++;112         do {113             v = stk[top--];114             instk[v] = 0;115             belong[v] = bcnt;116             cnt[bcnt]++;117         } while(v != u);118     }119 }120 121 LL quickmul(LL x, LL n) {122     LL ans = 1;123     while(n) {124         if(n & 1) ans = (ans * x) % mod;125         x = x * x % mod;126         n >>= 1;127     }128     return ans;129 }130 131 132 int main() {133     // FRead();134     while(~Rint(n)) {135         ret = 1; Cls(cnt);136         init();137         int v;138         For(i, 1, n+1) {139             Rint(v);140             adde(i, v);141         }142         For(i, 1, n+1) if(!dfn[i]) tarjan(i);143         LL tmp = 0;144         For(i, 1, bcnt+1) {145             if(cnt[i] > 1) {146                 ret = (ret * (quickmul(2, cnt[i])-2+mod))%mod;147                 tmp = (tmp + cnt[i]) % mod;148             }149         }150         ret = (ret * quickmul(2, n-tmp)) % mod;151         cout << ret << endl;152     }153     RT 0;154 }