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

#include <bits/stdc++.h>
// ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// clock_t start=clock();clock_t
// end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef pair<pii, int> ppii;
typedef pair<int, pii> pipi;
typedef pair<ll, ll> pll;
typedef pair<pll, ll> ppll;
typedef pair<ll, pll> plpl;
typedef pair<pii, pii> P;
typedef tuple<ll, ll, ll> tl;
typedef pair<double, double> pdd;
typedef vector<vector<ll>> mat;
ll mod = 1000000007;
ll mod2 = 998244353;
ll mod3 = 1000003;
ll mod4 = 998244853;
ll mod5 = 1000000009;
ll inf = 1LL << 62;
int iinf = 1 << 30;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-14;
#define rep(i, m, n) for (int i = m; i < n; i++)
#define rrep(i, n, m) for (ll i = n; i >= m; i--)
#define srep(itr, st) for (auto itr = st.begin(); itr != st.end(); itr++)
#define mrep(itr, mp) for (auto &itr : mp)
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    // http://xorshift.di.unimi.it/splitmix64.c
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
#define umh unordered_map<ll, ll, custom_hash>
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
  ll c = gcd(a, b);
  return a * b / c;
}
ll Pow(ll n, ll k) {
  if (k < 0)
    return 0;
  ll ret = 1;
  ll now = n;
  while (k > 0) {
    if (k & 1)
      ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
ll beki(ll n, ll k, ll md) {
  ll ret = 1;
  ll now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
ll gyaku(ll n, ll md) { return beki(n, md - 2, md); }
ll poc(ll n) {
  ll ret = 0;
  ll u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}
struct UF {
private:
  vector<int> par, len, you;

public:
  UF(int n) {
    rep(i, 0, n) {
      par.push_back(i);
      len.push_back(0);
      you.push_back(1);
    }
  }
  int root(int n) {
    if (par[n] == n)
      return n;
    else
      return par[n] = root(par[n]);
  }
  void unit(int a, int b) {
    a = root(a);
    b = root(b);
    if (a == b)
      return;
    if (len[a] < len[b]) {
      par[a] = b;
      you[b] += you[a];
    } else {
      par[b] = a;
      you[a] += you[b];
      if (len[a] == len[b])
        len[a]++;
    }
  }
  int yo(int a) {
    a = root(a);
    return you[a];
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  int p[n * n];
  rep(i, 0, n * n) {
    cin >> p[i];
    p[i]--;
  }
  int r[n][n];
  bool used[n][n];
  rep(i, 0, n) {
    rep(j, 0, n) {
      r[i][j] = min(min(i, n - i - 1), min(j, n - j - 1));
      used[i][j] = true;
    }
  }
  int ans = 0;
  rep(i, 0, n * n) {
    int h = p[i] / n, w = p[i] % n;
    ans += r[h][w];
    queue<pii> q;
    q.push({h, w});
    used[h][w] = false;
    while (q.size() > 0) {
      pii p = q.front();
      q.pop();
      int nh = p.first, nw = p.second;
      int t = r[nh][nw] + used[nh][nw];
      rep(j, 0, 4) {
        int nnh = nh + dh[j], nnw = nw + dw[j];
        if (nnh < 0 || nnh >= n || nnw < 0 || nnw >= n)
          continue;
        if (r[nnh][nnw] > t) {
          r[nnh][nnw] = t;
          q.push({nnh, nnw});
        }
      }
    }
  }
  cout << ans << endl;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
// ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// clock_t start=clock();clock_t
// end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef pair<pii, int> ppii;
typedef pair<int, pii> pipi;
typedef pair<ll, ll> pll;
typedef pair<pll, ll> ppll;
typedef pair<ll, pll> plpl;
typedef pair<pii, pii> P;
typedef tuple<ll, ll, ll> tl;
typedef pair<double, double> pdd;
typedef vector<vector<ll>> mat;
ll mod = 1000000007;
ll mod2 = 998244353;
ll mod3 = 1000003;
ll mod4 = 998244853;
ll mod5 = 1000000009;
ll inf = 1LL << 62;
int iinf = 1 << 30;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-14;
#define rep(i, m, n) for (int i = m; i < n; i++)
#define rrep(i, n, m) for (ll i = n; i >= m; i--)
#define srep(itr, st) for (auto itr = st.begin(); itr != st.end(); itr++)
#define mrep(itr, mp) for (auto &itr : mp)
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    // http://xorshift.di.unimi.it/splitmix64.c
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
#define umh unordered_map<ll, ll, custom_hash>
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
  ll c = gcd(a, b);
  return a * b / c;
}
ll Pow(ll n, ll k) {
  if (k < 0)
    return 0;
  ll ret = 1;
  ll now = n;
  while (k > 0) {
    if (k & 1)
      ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
ll beki(ll n, ll k, ll md) {
  ll ret = 1;
  ll now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
ll gyaku(ll n, ll md) { return beki(n, md - 2, md); }
ll poc(ll n) {
  ll ret = 0;
  ll u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}
struct UF {
private:
  vector<int> par, len, you;

public:
  UF(int n) {
    rep(i, 0, n) {
      par.push_back(i);
      len.push_back(0);
      you.push_back(1);
    }
  }
  int root(int n) {
    if (par[n] == n)
      return n;
    else
      return par[n] = root(par[n]);
  }
  void unit(int a, int b) {
    a = root(a);
    b = root(b);
    if (a == b)
      return;
    if (len[a] < len[b]) {
      par[a] = b;
      you[b] += you[a];
    } else {
      par[b] = a;
      you[a] += you[b];
      if (len[a] == len[b])
        len[a]++;
    }
  }
  int yo(int a) {
    a = root(a);
    return you[a];
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  int p[n * n];
  rep(i, 0, n * n) {
    cin >> p[i];
    p[i]--;
  }
  int r[n][n];
  rep(i, 0, n) { rep(j, 0, n) r[i][j] = 1; }
  int ans = 0;
  vector<pii> v;
  bool used[n][n];
  memset(used, false, sizeof used);
  rep(i, 0, n * n) {
    // cout<<i<<endl;
    deque<pipi> dq;
    int num = p[i];
    dq.push_back({0, {num / n, num % n}});
    used[num / n][num % n] = true;
    v.clear();
    v.push_back({num / n, num % n});
    for (;;) {
      pipi p = dq.front();
      dq.pop_front();
      int dis = p.first, nh = p.second.first, nw = p.second.second;
      if (nh == 0 || nh == n - 1 || nw == 0 || nw == n - 1) {
        ans += dis;
        break;
      }

      rep(j, 0, 4) {
        int nnh = nh + dh[j], nnw = nw + dw[j];
        if (used[nnh][nnw])
          continue;
        if (r[nnh][nnw] == 0) {
          dq.push_front({dis, {nnh, nnw}});
          used[nnh][nnw] = true;
          v.push_back({nnh, nnw});
        } else {
          dq.push_back({dis + 1, {nnh, nnw}});
          used[nnh][nnw] = true;
          v.push_back({nnh, nnw});
        }
      }
    }
    rep(j, 0, v.size()) used[v[j].first][v[j].second] = false;
    r[num / n][num % n] = 0;
  }
  cout << ans << endl;
}