func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int t;     t = 1;     while (t--) {       long long int n;       cin >> n;       long long int arr[n + 1];       long long int ans[n + 1];       unordered_map<long long int, long long int> mp;       arr[0] = 0;       for (__typeof(n + 1) i = (1) - ((1) > (n + 1));            i != (n + 1) - ((1) > (n + 1)); i += 1 - 2 * ((1) > (n + 1))) {         cin >> arr[i];         mp[arr[i]] = 1;       }       long long int p = 0;       for (__typeof(n + 1) i = (1) - ((1) > (n + 1));            i != (n + 1) - ((1) > (n + 1)); i += 1 - 2 * ((1) > (n + 1))) {         if (arr[i] != arr[i - 1]) {           ans[i] = arr[i - 1];           mp[arr[i - 1]] = 1;           continue;         }         while (mp[p]) {           p++;         }         ans[i] = p;         mp[p] = 1;       }       for (__typeof(n + 1) i = (1) - ((1) > (n + 1));            i != (n + 1) - ((1) > (n + 1)); i += 1 - 2 * ((1) > (n + 1)))         cout << ans[i] <<    ;       cout << endl;     }     return 0;   }   