func_code_string: #include <bits/stdc++.h>   using namespace std;   long long s[110000], a[110000];   int main() {     int n;     scanf( %d , &n);     a[0] = 1;     for (int i = 1; i <= 500; i++) a[i] = a[i - 1] * 2 % 1000000007;     memset(s, 0, sizeof(s));     for (int i = 1; i <= n; i++) {       int x;       scanf( %d , &x);       if (x != -1) s[x]++;     }     long long now = 0;     for (int i = 1; i <= n; i++)       if (s[i] > 0) {         now = now + a[s[i]] - 1;         now = (now % 1000000007 + 1000000007) % 1000000007;       }     long long ans = a[n - 1] - 1 - now;     ans = (ans % 1000000007 + 1000000007) % 1000000007;     printf( %lld n , ans);     return 0;   }   