reverse prefix func

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> pref(n);
    for (int i = 0; i < n; ++i){
        cin >> pref[i];
    }
    char symb = 'a';
    vector<char> s = {'a'};
    for (int i = 1; i < n; ++i){
        if (pref[i] == pref[i-1] + 1){
            s.emplace_back(s[pref[i-1]]);
        } else {
            if (pref[i] == 0){
                ++symb;
                s.emplace_back(symb);
            } else {
                s.emplace_back(s[pref[i]] - 1);
            }
        }
    }
    for (auto el: s){
        cout << el;
    }
    return 0;
}