Problem p02792 (C++)

Buggy submission (status: Time Limit Exceeded):
/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author Rishabhdeep Singh
 */

// doot diddly donger cuckerino Hahahahahah
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace __gnu_cxx;
using namespace std;

// @formatter:off
#define PB push_back
#define EB emplace_back
#define F first
#define S second
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sz(x) (long long)(x).size()
#define IOS                                                                    \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(NULL);                                                               \
  cout << fixed << setprecision(12);
#define IN_REP                                                                 \
  int tt;                                                                      \
  cin >> tt;                                                                   \
  while (tt--)
#define sim template <typename T
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \
  sim > typename enable_if<sizeof dud<T>(0) x 1, debug &>::type operator<<(T i)
sim > struct rge {
  T b, e;
};
sim > rge<T> range(T i, T j) { return rge<T>{i, j}; }
sim > auto dud(T *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) {
    cerr << boolalpha << i;
    ris;
  }
  eni(==) { ris << range(all(i)); }
  sim, typename U dor(pair<U, T> d) {
    ris << "(" << d.first << ", " << d.second << ")";
  }
  sim dor(rge<T> d) {
    *this << "[";
    for (auto it = d.b; it != d.e; ++it)
      *this << ", " + 2 * (it == d.b) << *it;
    ris << "]";
  }
#else
  sim dor(const T &) { ris; }
#endif
};
#define pr(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vb = vector<bool>;

using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vpii = vector<pii>;
using vpll = vector<pll>;
template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

const ll MOD = (ll)1e9 + 7;
const ld PI = acos(-1);

template <typename T> T gcd(T x, T y) { return (y == 0) ? x : gcd(y, x % y); }
template <typename T> void mini(T &x, T y) { x = min(x, y); }
template <typename T> void maxi(T &x, T y) { x = max(x, y); }
template <typename T, typename U> string to_string(pair<T, U> p) {
  return to_string(p.F) + " " + to_string(p.S);
}
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
// @formatter:on

class DHandstand2 {
public:
  bool ok(int i, int j, int k) {
    string s = to_string(k);
    return s[0] - '0' == i and s.back() - '0' == j;
  }
  void solve(std::istream &cin, std::ostream &cout) {
    ll n;
    cin >> n;
    vvll c(10, vll(10, 0));
    for (int i = 0; i < 10; ++i) {
      for (int j = 0; j < 10; ++j) {
        for (int k = 1; k <= n; ++k) {
          c[i][j] += ok(i, j, k);
        }
      }
    }
    ll ans = 0;
    for (int i = 0; i < 10; ++i) {
      for (int j = 0; j < 10; ++j) {
        ans += c[i][j] * c[j][i];
      }
    }
    cout << ans << '\n';
  }
};

int main() {
  IOS;
  DHandstand2 solver;
  std::istream &in(std::cin);
  std::ostream &out(std::cout);
  solver.solve(in, out);
  return 0;
}


Fixed submission:
/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author Rishabhdeep Singh
 */

// doot diddly donger cuckerino Hahahahahah
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace __gnu_cxx;
using namespace std;

// @formatter:off
#define PB push_back
#define EB emplace_back
#define F first
#define S second
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sz(x) (long long)(x).size()
#define IOS                                                                    \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(NULL);                                                               \
  cout << fixed << setprecision(12);
#define IN_REP                                                                 \
  int tt;                                                                      \
  cin >> tt;                                                                   \
  while (tt--)
#define sim template <typename T
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \
  sim > typename enable_if<sizeof dud<T>(0) x 1, debug &>::type operator<<(T i)
sim > struct rge {
  T b, e;
};
sim > rge<T> range(T i, T j) { return rge<T>{i, j}; }
sim > auto dud(T *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) {
    cerr << boolalpha << i;
    ris;
  }
  eni(==) { ris << range(all(i)); }
  sim, typename U dor(pair<U, T> d) {
    ris << "(" << d.first << ", " << d.second << ")";
  }
  sim dor(rge<T> d) {
    *this << "[";
    for (auto it = d.b; it != d.e; ++it)
      *this << ", " + 2 * (it == d.b) << *it;
    ris << "]";
  }
#else
  sim dor(const T &) { ris; }
#endif
};
#define pr(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vb = vector<bool>;

using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vpii = vector<pii>;
using vpll = vector<pll>;
template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

const ll MOD = (ll)1e9 + 7;
const ld PI = acos(-1);

template <typename T> T gcd(T x, T y) { return (y == 0) ? x : gcd(y, x % y); }
template <typename T> void mini(T &x, T y) { x = min(x, y); }
template <typename T> void maxi(T &x, T y) { x = max(x, y); }
template <typename T, typename U> string to_string(pair<T, U> p) {
  return to_string(p.F) + " " + to_string(p.S);
}
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
// @formatter:on

class DHandstand2 {
public:
  bool ok(int i, int j, int k) {
    string s = to_string(k);
    return s[0] - '0' == i and s.back() - '0' == j;
  }
  void solve(std::istream &cin, std::ostream &cout) {
    ll n;
    cin >> n;
    vvll c(10, vll(10, 0));
    for (int i = 1; i <= n; ++i) {
      string s = to_string(i);
      c[s[0] - '0'][s.back() - '0']++;
    }
    ll ans = 0;
    for (int i = 0; i < 10; ++i) {
      for (int j = 0; j < 10; ++j) {
        ans += c[i][j] * c[j][i];
      }
    }
    cout << ans << '\n';
  }
};

int main() {
  IOS;
  DHandstand2 solver;
  std::istream &in(std::cin);
  std::ostream &out(std::cout);
  solver.solve(in, out);
  return 0;
}