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

#define LOCAL
#define _USE_MATH_DEFINES
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

template <typename A, typename B>
ostream &operator<<(ostream &out, const pair<A, B> &a) {
  out << "(" << a.first << "," << a.second << ")";
  return out;
}
template <typename T, size_t N>
ostream &operator<<(ostream &out, const array<T, N> &a) {
  out << "[";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << "[";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T, class Cmp>
ostream &operator<<(ostream &out, const set<T, Cmp> &a) {
  out << "{";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "}";
  return out;
}
template <typename U, typename T, class Cmp>
ostream &operator<<(ostream &out, const map<U, T, Cmp> &a) {
  out << "{";
  bool first = true;
  for (auto &p : a) {
    out << (first ? "" : ", ");
    out << p.first << ":" << p.second;
    first = 0;
  }
  out << "}";
  return out;
}
#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}

typedef long long int64;
typedef pair<int, int> ii;
const int INF = 1 << 29;
const int MOD = 1e9 + 7;
mt19937 mrand(random_device{}());
int rnd(int x) { return mrand() % x; }

struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
  };
} fast_ios_;

const int d[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
const int N = 500;
bool visit[N][N];
int dp[N][N];
int n;

void BFS(int x, int y) {
  queue<ii> Q;
  Q.push({x, y});
  while (!Q.empty()) {
    int x = Q.front().first, y = Q.front().second;
    Q.pop();
    for (int k = 0; k < 4; ++k) {
      int nx = x + d[k][0];
      int ny = y + d[k][1];
      if (nx < 0 || nx >= n || ny < 0 || ny >= n)
        continue;
      if (dp[nx][ny] > dp[x][y] + !visit[x][y]) {
        dp[nx][ny] = dp[x][y] + !visit[x][y];
        Q.push({nx, ny});
      }
    }
  }
}

int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      dp[i][j] = min(min(i, j), min(n - 1 - i, n - 1 - j));
    }
  }
  int64 ret = 0;
  for (int i = 0; i < n * n; ++i) {
    int pos;
    scanf("%d", &pos);
    --pos;
    int x = pos / n, y = pos % n;
    // trace(x, y, dp[x][y]);
    ret += dp[x][y];
    visit[x][y] = true;
    BFS(x, y);
  }
  printf("%lld\\n", ret);
  return 0;
}


Error: TLE

Fixed submission:

#define LOCAL
#define _USE_MATH_DEFINES
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

template <typename A, typename B>
ostream &operator<<(ostream &out, const pair<A, B> &a) {
  out << "(" << a.first << "," << a.second << ")";
  return out;
}
template <typename T, size_t N>
ostream &operator<<(ostream &out, const array<T, N> &a) {
  out << "[";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << "[";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T, class Cmp>
ostream &operator<<(ostream &out, const set<T, Cmp> &a) {
  out << "{";
  bool first = true;
  for (auto &v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "}";
  return out;
}
template <typename U, typename T, class Cmp>
ostream &operator<<(ostream &out, const map<U, T, Cmp> &a) {
  out << "{";
  bool first = true;
  for (auto &p : a) {
    out << (first ? "" : ", ");
    out << p.first << ":" << p.second;
    first = 0;
  }
  out << "}";
  return out;
}
#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}

typedef long long int64;
typedef pair<int, int> ii;
const int INF = 1 << 29;
const int MOD = 1e9 + 7;
mt19937 mrand(random_device{}());
int rnd(int x) { return mrand() % x; }

struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
  };
} fast_ios_;

const int d[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
const int N = 500;
bool visit[N][N];
int dp[N][N], h[N][N];
int n;

int solve(int x, int y) {
  deque<ii> Q;
  dp[x][y] = 0;
  Q.push_back({x, y});
  vector<ii> footprint;
  int ret = INF;
  while (!Q.empty()) {
    int x = Q.front().first, y = Q.front().second;
    Q.pop_front();
    footprint.push_back({x, y});
    if (x == 0 || x == n - 1 || y == 0 || y == n - 1) {
      ret = min(ret, dp[x][y]);
    }
    for (int k = 0; k < 4; ++k) {
      int nx = x + d[k][0];
      int ny = y + d[k][1];
      if (nx < 0 || nx >= n || ny < 0 || ny >= n)
        continue;
      if (visit[nx][ny]) {
        if (dp[nx][ny] > dp[x][y]) {
          dp[nx][ny] = dp[x][y];
          Q.push_front({nx, ny});
        }
      } else {
        if (dp[nx][ny] > dp[x][y] + 1) {
          dp[nx][ny] = dp[x][y] + 1;
          Q.push_back({nx, ny});
        }
      }
    }
  }
  for (auto &p : footprint) {
    int x = p.first, y = p.second;
    dp[x][y] = INF;
  }
  return ret;
}

int main() {
  scanf("%d", &n);
  int64 ret = 0;
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      dp[i][j] = INF;
    }
  }
  for (int i = 0; i < n * n; ++i) {
    int pos;
    scanf("%d", &pos);
    --pos;
    int x = pos / n, y = pos % n;
    int cur = solve(x, y);
    // trace(x, y, cur);
    ret += cur;
    visit[x][y] = true;
  }
  printf("%lld\\n", ret);
  return 0;
}