Problem p02792 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cfloat>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits.h>
#include <list>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

using namespace std;
#define int long long
#define ll long long
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define FORR(i, a, b) for (ll i = (a); i <= (b); i++)
#define repr(i, n) for (ll i = n; i >= 0; i--)
#define P pair<ll, ll>
#define sz(x) (ll) x.size()
#define ALL(x) (x).begin(), (x).end()
#define ALLR(x) (x).rbegin(), (x).rend()
#define VE vector<ll>
#define COUT(x) cout << (x) << endl
#define MA map<ll, ll>
#define SE set<ll>
#define PQ priority_queue<ll>
#define PQR priority_queue<ll, VE, greater<ll>>
#define COUT(x) cout << (x) << endl
#define YES(n) cout << ((n) ? "YES" : "NO") << endl
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl
#define EPS (1e-10)
#define pb push_back

const long long MOD = 1000000007;
// const long long MOD = 998244353;
const long long INF = 1LL << 60;
const double PI = acos(-1.0);

long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return a * b / g;
}
bool prime(ll n) {
  for (ll i = 2; i <= sqrt(n); i++) {
    if (n % i == 0)
      return false;
  }
  return n != 1;
}
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

const int MAX_N = 100010;

int dp[10][10];

signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  rep(i, 9) {
    rep(j, 9) {
      int k = i + 1;
      int l = j + 1;
      for (int a = 1; a <= n; a++) {
        string tmp = to_string(a);
        int b = tmp[0] - '0';
        int c = tmp[tmp.size() - 1] - '0';
        if (b == 0 || c == 0)
          continue;
        if (k == c && l == b) {
          dp[i][j]++;
        }
      }
    }
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    string s = to_string(i);
    int a = s[0] - '0';
    int b = s[s.size() - 1] - '0';
    if (a == 0 || b == 0)
      continue;
    ans += dp[a - 1][b - 1];
  }
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cfloat>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits.h>
#include <list>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

using namespace std;
#define int long long
#define ll long long
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define FORR(i, a, b) for (ll i = (a); i <= (b); i++)
#define repr(i, n) for (ll i = n; i >= 0; i--)
#define P pair<ll, ll>
#define sz(x) (ll) x.size()
#define ALL(x) (x).begin(), (x).end()
#define ALLR(x) (x).rbegin(), (x).rend()
#define VE vector<ll>
#define COUT(x) cout << (x) << endl
#define MA map<ll, ll>
#define SE set<ll>
#define PQ priority_queue<ll>
#define PQR priority_queue<ll, VE, greater<ll>>
#define COUT(x) cout << (x) << endl
#define YES(n) cout << ((n) ? "YES" : "NO") << endl
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl
#define EPS (1e-10)
#define pb push_back

const long long MOD = 1000000007;
// const long long MOD = 998244353;
const long long INF = 1LL << 60;
const double PI = acos(-1.0);

long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return a * b / g;
}
bool prime(ll n) {
  for (ll i = 2; i <= sqrt(n); i++) {
    if (n % i == 0)
      return false;
  }
  return n != 1;
}
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

const int MAX_N = 100010;

int dp[10][10];

signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;

  for (int a = 1; a <= n; a++) {
    string tmp = to_string(a);
    int b = tmp[0] - '0';
    int c = tmp[tmp.size() - 1] - '0';
    // cout << a << endl;
    if (b == 0 || c == 0)
      continue;
    dp[c - 1][b - 1]++;
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    string s = to_string(i);
    int a = s[0] - '0';
    int b = s[s.size() - 1] - '0';
    if (a == 0 || b == 0)
      continue;
    ans += dp[a - 1][b - 1];
  }
  cout << ans << endl;
  return 0;
}