Problem p02629 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define mp make_pair
#define pb(x) push_back(x)
#define vi vector<int>
#define vs vector<string>
#define vll vector<long long>
#define vc vector<char>
#define vs vector<string>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pil pair<int, long long>
#define pli pair<long long, int>
#define pcc pair<char, char>
#define pdd pair<double, double>
#define mll map<long long, long long>
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define flsh fflush(stdout)
#define gcd __gcd
#define clr(x) memset(x, 0, sizeof(x))
#define mod 1000000007LL
#define mod2 998244353LL
#define INF 1000000000007

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef tree<ll, null_type, less<ll>, rb_tree_tag,
             tree_order_statistics_node_update>
    o_tree;

void solve() {
  ll n;
  cin >> n;

  ll no = 0;
  vll v;
  while (n > 0) {
    n--;
    v.pb(n % 26);
    n /= 26;
  }
  //    for(auto it:v)
  //    {
  //        cout<<it<<" ";
  //    }
  reverse(all(v));
  for (auto it : v) {
    cout << (char)(it + 'a');
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
  cout << setprecision(20);

  ll t = 1;

  // cin>>t;

  while (t--) {
    solve();
  }

  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define mp make_pair
#define pb(x) push_back(x)
#define vi vector<int>
#define vs vector<string>
#define vll vector<long long>
#define vc vector<char>
#define vs vector<string>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pil pair<int, long long>
#define pli pair<long long, int>
#define pcc pair<char, char>
#define pdd pair<double, double>
#define mll map<long long, long long>
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define flsh fflush(stdout)
#define gcd __gcd
#define clr(x) memset(x, 0, sizeof(x))
#define mod 1000000007LL
#define mod2 998244353LL
#define INF 1000000000007

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef tree<ll, null_type, less<ll>, rb_tree_tag,
             tree_order_statistics_node_update>
    o_tree;

void solve() {
  ll n;
  cin >> n;
  ll no = 0;
  ll no1 = 1;
  ll no2 = 0;
  ll i, j;
  vll v;
  n--;
  while (n > 0) {
    v.pb(n % 26);
    n /= 26;
  }
  reverse(all(v));
  for (i = 0; i < v.size(); i++) {
    v[i]--;
  }
  v[v.size() - 1]++;
  for (auto it : v) {
    cout << (char)(it + 'a');
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
  cout << setprecision(20);

  ll t = 1;

  // cin>>t;

  while (t--) {
    solve();
  }

  return 0;
}