func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 1e5 + 5;   int a[maxn], b[maxn];   bool v[maxn];   int main() {     int n;     cin >> n;     a[0] = -1;     for (int i = 1; i <= n; ++i) {       cin >> a[i];       v[a[i]] = 1;       if (a[i] > a[i - 1])         b[i] = a[i - 1];       else         b[i] = -1;     }     int c = 0;     for (int i = 1; i <= n; ++i) {       if (b[i] == -1) {         while (v[c]) c++;         b[i] = c++;       }     }     for (int i = 1; i <= n; ++i) cout << b[i] <<    ;     return 0;   }   