func_code_string: #include <bits/stdc++.h>   const int MOD = int(1E9) + 7;   const int MAXN = 100000;   int pw[MAXN + 5], cnt[MAXN + 5];   void init() {     pw[0] = 1;     for (int i = 1; i <= MAXN; i++) pw[i] = 2LL * pw[i - 1] % MOD;   }   int main() {     init();     int n, x;     scanf( %d , &n);     for (int i = 1; i <= n; i++) {       scanf( %d , &x);       if (x != -1) cnt[x]++;     }     int ans = pw[n - 1] - 1;     for (int i = 1; i <= n; i++) ans = (ans - 1LL * (pw[cnt[i]] - 1) % MOD) % MOD;     printf( %d n , (ans + MOD) % MOD);   }   