func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mo = (int)1e9 + 7;   const int maxn = 1000010;   int n;   long long fac[maxn], ans;   int a[maxn], num[maxn], num1[maxn], pos[maxn], mul[maxn];   int pre[maxn], ne[maxn];   vector<int> v[maxn];   inline void init() {     fac[0] = 1;     for (int i = 1; i <= n + 2; ++i) fac[i] = fac[i - 1] * i % mo, mul[i] = 1;     for (int i = 2; i <= n; ++i) {       if (!v[i].size()) {         num[n / i]++;         pos[i] = n / i;         for (int j = i; j <= n; j += i) v[j].push_back(i), mul[j] *= i;       }     }     for (int i = 1; i <= n; ++i) num1[mul[i]]++;     num[1]++;     pos[1] = 1;     v[1].push_back(1);   }   int main() {     scanf( %d , &n);     init();     for (int i = 1; i <= n; ++i) scanf( %d , &a[i]);     for (int i = 1; i <= n; ++i)       if (a[i]) {         num1[mul[a[i]]]--;         if (v[a[i]].size() != v[i].size()) return puts( 0 ), 0;         for (int j = 0; j < v[i].size() - 1; j++)           if (v[a[i]][j] != v[i][j]) return puts( 0 ), 0;         long long x = v[a[i]].back(), y = v[i].back();         if (pos[x] != pos[y]) return puts( 0 ), 0;         if (pre[x] && pre[x] != y) return puts( 0 ), 0;         if (ne[y] && ne[y] != x) return puts( 0 ), 0;         if (!pre[x] && !ne[y]) num[pos[x]]--;         pre[x] = y;         ne[y] = x;       }     ans = 1;     for (int i = 1; i <= n; ++i)       ans = ans * fac[num[i]] % mo, ans = ans * fac[num1[i]] % mo;     printf( %lld n , ans);     return 0;   }   