Language: C++

#include<bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
typedef long long ll;
const ll MOD = 1e9+7;
#define rep(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)
#define REP(i,num,n) for(int i=num, i##_len=(n); i<i##_len; ++i)
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<class T> inline void add(T &a, T b){a = ((a+b) % MOD + MOD) % MOD;};
#define print(x) (cout << (x) << endl)
#define pb push_back
#define mp make_pair
#define sz(x) int(x.size())
template<class T> inline void Yes(T condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
template<class itr> void cins(itr first, itr last){ for(auto i = first; i != last; i++){ cin >> (*i); } }
template<class itr> void array_output(itr start, itr goal){ string ans; for(auto i = start; i != goal; i++) ans += to_string(*i) + " "; if(!ans.empty()) ans.pop_back(); cout << ans << endl; }
#define fs first
#define sc second


const int INF = 1e9;
const ll LLINF = 1e16;

template<typename T>
vector<T> make_v(size_t a){return vector<T>(a);}
 
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}
 
template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value!=0>::type
fill_v(U &u,const V... v){u=U(v...);}
 
template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value==0>::type
fill_v(U &u,const V... v){
  for(auto &e:u) fill_v<T>(e,v...);
}
 
template<typename T>
T gcd(T a,T b){return b?gcd(b,a%b):a;}

template<typename T>
T ngcd(vector<T> a){
    T res;
    res = a[0];
    for(int i = 1; i < a.size() && res != 1; i++) {
        res = gcd(a[i], res);
    }
    return res;
}
 
template<typename T>
T lcm(T a, T b) {
    return a / gcd(a, b) * b;
}

template<typename T>
T nlcm(vector<T> numbers) {
    T res;
    res = numbers[0];
    for (int i = 1; i < numbers.size(); i++) {
        res = lcm(res, numbers[i]);
    }
    return res;
}


// 素数判定
template<typename T>
bool isPrime(T x){
    T i;
    if(x < 2)return 0;
    else if(x == 2) return 1;
    if(x%2 == 0) return 0;
    for(i = 3; i*i <= x; i += 2) if(x%i == 0) return 0;
    return 1;
}

// 桁和
template<typename T>
T digsum(T n) {
    T res = 0;
    while(n > 0) {
        res += n%10;
        n /= 10;
    }
    return res;
}

// 回文判定
bool kai (string s) {
    string t{s};
    reverse(begin(t), end(t));
    return s == t;
};

// 指定した文字cが文字列に何文字入ってるか
ll stringcount(string s, char c) {
    return count(s.cbegin(), s.cend(), c);
}



// 割り算の切り上げ処理
template<typename T>
T rp(T a, T b) {
  return (a + b - 1) / b;
}


using pint = pair<int, int>;
using pll = pair<ll, ll>;

template<int MOD> struct Fp {
    long long val;
    constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator += (const Fp& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator < (const Fp& x) const {
        return this->val < x.val;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
 
using mint = Fp<MOD>;

int main(void)
{
    cout.tie(0);
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    int n;
    cin >> n;
    map<int,int> mp;
    string prev = "";
    rep(i, n){
        string w;
        cin >> w;
        if(prev != ""){
            if(prev[sz(prev) - 1] != w[0]){
                print("No");
                return 0;
            }
        }
        mp[w]++;
        if(mp[w] > 1){
            print("No");
            return 0;
        }

    }
    print("Yes");

}



Compiler output:
a.cc: In function 'int main()':
a.cc:200:11: error: no match for 'operator[]' (operand types are 'std::map<int, int>' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
  200 |         mp[w]++;
      |           ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >; mapped_type = int; key_type = int]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'const std::map<int, int>::key_type&' {aka 'const int&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >; mapped_type = int; key_type = int]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'std::map<int, int>::key_type&&' {aka 'int&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~
a.cc:201:14: error: no match for 'operator[]' (operand types are 'std::map<int, int>' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
  201 |         if(mp[w] > 1){
      |              ^
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >; mapped_type = int; key_type = int]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'const std::map<int, int>::key_type&' {aka 'const int&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >; mapped_type = int; key_type = int]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'std::map<int, int>::key_type&&' {aka 'int&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~