//@formatter:off #include #define overload4(_1,_2,_3,_4,name,...) name #define rep1(i,n) for (ll i = 0; i < ll(n); ++i) #define rep2(i,s,n) for (ll i = ll(s); i < ll(n); ++i) #define rep3(i,s,n,d) for(ll i = ll(s); i < ll(n); i+=d) #define rep(...) overload4(__VA_ARGS__,rep3,rep2,rep1)(__VA_ARGS__) #define rrep1(i,n) for (ll i = ll(n)-1; i >= 0; i--) #define rrep2(i,n,t) for (ll i = ll(n)-1; i >= (ll)t; i--) #define rrep3(i,n,t,d) for (ll i = ll(n)-1; i >= (ll)t; i-=d) #define rrep(...) overload4(__VA_ARGS__,rrep3,rrep2,rrep1)(__VA_ARGS__) #define all(a) a.begin(),a.end() #define rall(a) a.rbegin(),a.rend() #define popcount(x) __builtin_popcount(x) #define pb push_back #define eb emplace_back #ifdef __LOCAL #define debug(...) { cout << #__VA_ARGS__; cout << ": "; print(__VA_ARGS__); cout << flush; } #else #define debug(...) void(0) #endif #define INT(...) int __VA_ARGS__;scan(__VA_ARGS__) #define LL(...) ll __VA_ARGS__;scan(__VA_ARGS__) #define STR(...) string __VA_ARGS__;scan(__VA_ARGS__) #define CHR(...) char __VA_ARGS__;scan(__VA_ARGS__) #define DBL(...) double __VA_ARGS__;scan(__VA_ARGS__) #define LD(...) ld __VA_ARGS__;scan(__VA_ARGS__) using namespace std; using ll = long long; using ld = long double; using P = pair; using LP = pair; using vi = vector; using vvi = vector>; using vl = vector; using vvl = vector>; using vd = vector; using vvd = vector>; using vs = vector; using vc = vector; using vvc = vector>; using vb = vector; using vvb = vector>; using vp = vector

; using vvp = vector>; template istream& operator>>(istream &is,pair &p) { return is >> p.first >> p.second; } template ostream& operator<<(ostream &os,const pair &p) { return os<<'{'< istream& operator>>(istream &is,vector &v) { for(T &t:v){is>>t;} return is; } template ostream& operator<<(ostream &os,const vector &v) { os<<'[';rep(i,v.size())os< void vecout(const vector &v,char div='\n') { rep(i,v.size()) cout< bool chmin(T& a,T b) {if(a > b){a = b; return true;} return false;} template bool chmax(T& a,T b) {if(a < b){a = b; return true;} return false;} void scan(){} template void scan(Head& head, Tail&... tail){ cin >> head; scan(tail...); } template void print(const T& t){ cout << t << '\n'; } template void print(const Head& head, const Tail&... tail){ cout< void fin(const T&... a) { print(a...); exit(0); } const string yes[] = {"no","yes"}; const string Yes[] = {"No","Yes"}; const string YES[] = {"NO","YES"}; const int inf = 1001001001; const ll linf = 1001001001001001001; //@formatter:on constexpr int mod = 1000000007; //constexpr int mod = 998244353; struct mint { ll x; constexpr mint(ll x = 0) : x((x % mod + mod) % mod) {} constexpr mint operator-() const { return mint(-x); } constexpr mint &operator+=(const mint &a) { if ((x += a.x) >= mod) x -= mod; return *this; } constexpr mint &operator++() { return *this += mint(1); } constexpr mint &operator-=(const mint &a) { if ((x += mod - a.x) >= mod) x -= mod; return *this; } constexpr mint &operator--() { return *this -= mint(1); } constexpr mint &operator*=(const mint &a) { (x *= a.x) %= mod; return *this; } constexpr mint operator+(const mint &a) const { mint res(*this); return res += a; } constexpr mint operator-(const mint &a) const { mint res(*this); return res -= a; } constexpr mint operator*(const mint &a) const { mint res(*this); return res *= a; } constexpr mint pow(ll t) const { mint res = mint(1), a(*this); while (t > 0) { if (t & 1) res *= a; t >>= 1; a *= a; } return res; } // for prime mod constexpr mint inv() const { return pow(mod - 2); } constexpr mint &operator/=(const mint &a) { return *this *= a.inv(); } constexpr mint operator/(const mint &a) const { mint res(*this); return res /= a; } }; ostream &operator<<(ostream &os, const mint &a) { return os << a.x; } bool operator==(const mint &a, const mint &b) { return a.x == b.x; } bool operator!=(const mint &a, const mint &b) { return a.x != b.x; } bool operator==(const mint &a, const int &b) { return a.x == b; } bool operator!=(const mint &a, const int &b) { return a.x != b; } class combination { public: vector fact, ifact; combination(int n) : fact(n + 1), ifact(n + 1) { assert(n < mod); fact[0] = 1; for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i; ifact[n] = fact[n].inv(); for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i; } mint operator()(int n, int k) { if (k < 0 || k > n) return 0; return fact[n] * ifact[k] * ifact[n - k]; } } comb(100010); int main() { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); INT(n); vi p(n); cin >> p; rep(i, n) --p[i]; vi v(n + 1); vb seen(n); rep(i, n) { if (seen[i]) continue; int now = i; int len = 0; do { seen[now] = true; len++; now = p[now]; } while (now != i); v[len]++; } mint ans = 1; int rem = n; rep(i, 1, n + 1) { if (!v[i]) continue; rep(_, v[i]) { ans *= comb(rem, i); rem -= i; ans *= comb.fact[i - 1]; } ans *= comb.ifact[v[i]]; } assert(rem == 0); fin(ans); }