Problem p03261 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
///////////////////////////////////////////
const long long int INF = 1LL << 60;
const long long int Mod = 1000000007;
using ll = long long int;
using ci = const int;
using vi = vector<int>;
using Vi = vector<long long int>;
using P = pair<int, int>;
using PLL = pair<ll, ll>;
using matrix = vector<vector<ll>>;
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)
#define all(x) (x).begin(), (x).end()
#define rp(i, N) for (ll i = 0; i < (ll)N; i++)
#define repi(i, a, b) for (ll i = ll(a); i < ll(b); ++i)
template <class T> bool chmax(T &former, const T &b) {
  if (former < b) {
    former = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &former, const T &b) {
  if (b < former) {
    former = b;
    return true;
  }
  return false;
}
template <class T> T sqar(T x) { return x * x; } // sqrt(x)は平方根;
#define Sort(v)                                                                \
  std::sort(v.begin(), v.end(),                                                \
            std::greater<decltype(v[0])>()) // 降順でVをソート
#define p_queue(v) priority_queue<v, vector<v>, greater<v>>
template <class T> inline void princ(T x) { cout << x << " "; };
template <class T> inline void print(T x) { cout << x << "\n"; };
template <class T> inline void Yes(T condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
template <class T> inline void YES(T condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
///////////////////////////////////////////////////////////////////////////////////

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(30);

  int n;
  cin >> n;
  vector<string> vs;
  char ch;
  bool ok = true;
  rp(i, n) {
    string w;
    cin >> w;
    vs.push_back(w);
    if (i >= 1 && ch != w[0]) {
      ok = false;
      break;
    }
    reverse(all(w));
    ch = w[0];
  }
  sort(all(vs));
  rp(i, n - 1) {
    if (vs[i] == vs[i + 1])
      ok = false;
  }
  Yes(ok);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
///////////////////////////////////////////
const long long int INF = 1LL << 60;
const long long int Mod = 1000000007;
using ll = long long int;
using ci = const int;
using vi = vector<int>;
using Vi = vector<long long int>;
using P = pair<int, int>;
using PLL = pair<ll, ll>;
using matrix = vector<vector<ll>>;
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)
#define all(x) (x).begin(), (x).end()
#define rp(i, N) for (ll i = 0; i < (ll)N; i++)
#define repi(i, a, b) for (ll i = ll(a); i < ll(b); ++i)
template <class T> bool chmax(T &former, const T &b) {
  if (former < b) {
    former = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &former, const T &b) {
  if (b < former) {
    former = b;
    return true;
  }
  return false;
}
template <class T> T sqar(T x) { return x * x; } // sqrt(x)は平方根;
#define Sort(v)                                                                \
  std::sort(v.begin(), v.end(),                                                \
            std::greater<decltype(v[0])>()) // 降順でVをソート
#define p_queue(v) priority_queue<v, vector<v>, greater<v>>
template <class T> inline void princ(T x) { cout << x << " "; };
template <class T> inline void print(T x) { cout << x << "\n"; };
template <class T> inline void Yes(T condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
template <class T> inline void YES(T condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
///////////////////////////////////////////////////////////////////////////////////

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(30);

  int n;
  cin >> n;
  vector<string> vs;
  char ch;
  bool ok = true;
  rp(i, n) {
    string w;
    cin >> w;
    vs.push_back(w);
    if (i >= 1 && ch != w[0]) {
      ok = false;
    }
    reverse(all(w));
    ch = w[0];
  }
  sort(all(vs));
  rp(i, n - 1) {
    if (vs[i] == vs[i + 1])
      ok = false;
  }
  Yes(ok);
  return 0;
}