Problem p02670 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))
#define sz(v) ((int)v.size())

using namespace std;

using i64 = long long;
using f80 = long double;
using vi32 = vector<int>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

void yes() {
  cout << "Yes" << endl;
  exit(0);
}
void no() {
  cout << "No" << endl;
  exit(0);
}
template <typename T>
class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T>
class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> void amax(T &x, T y) { x = max(x, y); }
template <typename T> void amin(T &x, T y) { x = min(x, y); }
template <typename T> T exp(T x, i64 n, T e = 1) {
  T r = e;
  while (n > 0) {
    if (n & 1)
      r *= x;
    x *= x;
    n >>= 1;
  }
  return r;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  rep(i, v.size()) {
    if (i)
      os << ' ';
    os << v[i];
  }
  return os;
}
void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(16);
  solve();
  return 0;
}

const int INF = 1001001001;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};

void solve() {
  int n;
  cin >> n;
  vi32 p(n * n);
  cin >> p;
  rep(i, n * n) { p[i]--; }
  vector<vi32> dp(n, vi32(n));
  rep(i, n) rep(j, n) { dp[i][j] = min({i, j, n - i - 1, n - j - 1}); }
  vector<vi32> f(n, vi32(n));
  int ans = 0;
  rep(i, n * n) {
    int x = p[i] % n;
    int y = p[i] / n;
    ans += dp[x][y];
    f[x][y] = 1;
    using T = tuple<int, int, int>;
    queue<T> q;
    rep(k, 4) {
      int nx = x + dx[k];
      int ny = y + dy[k];
      if (nx < 0 || nx >= n || ny < 0 || ny >= n)
        continue;
      q.emplace(nx, ny, dp[x][y]);
    }
    while (sz(q)) {
      int x, y, cost;
      tie(x, y, cost) = q.front();
      q.pop();
      if (dp[x][y] <= cost)
        continue;
      dp[x][y] = cost;
      rep(k, 4) {
        int nx = x + dx[k];
        int ny = y + dy[k];
        if (nx < 0 || nx >= n || ny < 0 || ny >= n)
          continue;
        q.emplace(nx, ny, cost + (f[x][y] ? 0 : 1));
      }
    }
  }
  cout << ans << endl;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))
#define sz(v) ((int)v.size())

using namespace std;

using i64 = long long;
using f80 = long double;
using vi32 = vector<int>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

void yes() {
  cout << "Yes" << endl;
  exit(0);
}
void no() {
  cout << "No" << endl;
  exit(0);
}
template <typename T>
class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T>
class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> void amax(T &x, T y) { x = max(x, y); }
template <typename T> void amin(T &x, T y) { x = min(x, y); }
template <typename T> T exp(T x, i64 n, T e = 1) {
  T r = e;
  while (n > 0) {
    if (n & 1)
      r *= x;
    x *= x;
    n >>= 1;
  }
  return r;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  rep(i, v.size()) {
    if (i)
      os << ' ';
    os << v[i];
  }
  return os;
}
void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(16);
  solve();
  return 0;
}

const int INF = 1001001001;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};

void solve() {
  int n;
  cin >> n;
  vi32 p(n * n);
  cin >> p;
  rep(i, n * n) p[i]--;
  vector<vi32> b(n, vi32(n));
  rep(i, n * n) {
    int x = p[i] % n;
    int y = p[i] / n;
    b[x][y] = i;
  }
  int ans = 0;
  vector<vi32> f(n, vi32(n));
  rep(i, n * n) {
    int x = p[i] % n;
    int y = p[i] / n;
    using T = tuple<int, int, int>;
    deque<T> q;
    q.emplace_front(x, y, 0);
    vector<pair<int, int>> history;
    int co = -1;
    while (sz(q)) {
      int x, y, cost;
      tie(x, y, cost) = q.front();
      q.pop_front();
      if (f[x][y])
        continue;
      f[x][y] = 1;
      history.emplace_back(x, y);
      if (x == 0 || x == n - 1 || y == 0 || y == n - 1) {
        co = cost;
        break;
      }
      rep(k, 4) {
        int nx = x + dx[k];
        int ny = y + dy[k];
        if (nx < 0 || nx >= n || ny < 0 || ny >= n)
          continue;
        if (b[nx][ny] < i) {
          q.emplace_front(nx, ny, cost);
        } else {
          q.emplace_back(nx, ny, cost + 1);
        }
      }
    }
    ans += co;
    for (auto h : history) {
      int x, y;
      tie(x, y) = h;
      f[x][y] = 0;
    }
  }
  cout << ans << endl;
}